[Clinical epidemiological characteristics of pertussis in children and the status of infection in their close contacts].

Objective: To investigate the clinical epidemiological characteristics of children with pertussis and the infection of their close contacts. Methods: The clinical data of children with pertussis and the etiological detection results of close contacts in Shenzhen Children's Hospital from 2015 to 2018 were collected and descriptive epidemiological analysis was carried out. Results: The cases of pertussis from 2015 to 2018 were reported as 504, 425, 796 and 991 respectively, with a total of 2 716 cases. The most cases was in May in 2015 (72 cases), in August in 2016 and 2018 (68 cases and 144 cases), and in July in 2017 (115 cases). A total of 1 517 male and 1 199 female children were reported from 2015 to 2018, the ratio of male-to-female was 1.3∶1. The proportion of children under 1 year old was 79.7% (2 165/2 716), of which 74.4% (1 610/2 165) was less than 6 months old. Among the reported cases, 1 605 (59.1%) were treated as outpatients, aged M(Q1,Q3) 5 (3, 11) months, and 1 111 (40.9%) were hospitalized, aged 4 (2, 7) months. There were 876 outpatients (54.4%) and 734 inpatients (45.6%) under 6 months of age, 575 outpatients (63.5%) and 331 inpatients (36.5%) between 6 months and 2 years of age, and 154 outpatients (77.0%) and 46 inpatients (23.0%) with above 2 years old, respectively. There were statistically significant differences between the two treatment methods in different age groups (P<0.001). The average hospitalization time of inpatients under 6 months of age was (8.5±3.9) days, that of inpatients between 6 months and 2 years of age was (7.1±3.7) days, and that of inpatients above 2 years old was (6.8±3.3) days. The difference was statistically significant (P<0.001). The etiological test results of pertussis were collected from 617 close contacts of 270 reported cases, the positive detection rate of mothers was the highest (34.9%). Conclusions: From 2015 to 2018, the number of reported cases of pertussis in our hospital fluctuated and increased year by year, with high incidence in summer, mainly in children under 1 year old, and more males than females. Outpatient treatment was more than inpatient treatment, its age was obviously older than the latter. The younger the children, the higher the proportion of hospitalization, and with the increase of the age, the hospitalization time was obviously shortened. Among the close family contacts, the mother might be the main source of pertussis infection in children.

[Clinical characteristics and related factors of human respiratory syncytial viruses infection in premature infants within 2 years after birth in Shenzhen Children's Hospital].

Objective: To analyze the clinical characteristics and factors associated with human respiratory syncytial virus (HRSV) infection in preterm infants within the first 2 years of life. Methods: Children with respiratory tract infections admitted to Shenzhen Children's Hospital during the 3-year period from January 2016 to December 2018 who were <2 years old and whose gestational age at birth was <37 weeks were selected, and those who met the diagnostic criteria for RSV infection were categorized as the positive case group, and those who had no detectable influenza virus, parainfluenza virus and adenovirus antigens were categorized as the negative group. The clinical characteristics of the case group were retrospectively analyzed. A multivariable logistic regression model was used to analyze the associated factors. Results: A total of 1, 483 children were included, of whom 149 (10.1%) were HRSV positive (case group) and 447 (30.1%) were in the negative group (control group). In the case group, there were 88 (59.1%) male and 61 (40.1%) female children; 127 children (85.2%) in the mild-to-moderate disease group and 22 children (14.8%) in the severe disease group. The number of cases in the severe disease group was greater than that in the mild-to-moderate disease group [(17 cases, 77.3%) than (59 cases, 46.5%)], with statistical significance (P=0.010). A total of 117 cases (78.5%) had onset from February to July. Multivariable analysis showed that males [OR (95%CI) of 0.105 (0.013-0.112)], age at month [0.045 (0.036-0.112)], congenital heart disease [0.388 (0.206-0.940)] and bronchopulmonary dysplasia [0.622 (0.484-0.927)] were positively associated with HRSV infection in preterm infants. Conclusion: The high prevalence of HRSV infection in preterm infants in Shenzhen is from February to July each year, and male children are more common. Young age, congenital heart disease and bronchopulmonary dysplasia are all independent risk factors for HRSV infection in preterm infants.

[A multicentric study on clinical characteristics and antibiotic sensitivity in children with methicillin-resistant Staphylococcus aureus infection].

Objective: To investigate the clinical characteristics of pediatric methicillin-resistant Staphylococcus aureus (MRSA) infection and the antibiotic sensitivity of the isolates. Methods: The clinical data of children with MRSA infection and antibiotic sensitivity of the isolates from 11 children's hospitals in Infectious Diseases Surveillance of Paediatrics (ISPED) group of China between January 1, 2018 and December 31, 2018 were collected retrospectively. The children's general condition, high-risk factors, antimicrobial therapy and prognosis, differences in clinical disease and laboratory test results between different age groups, and differences of antibiotic sensitivity between community-acquired (CA)-MRSA and hospital-acquired (HA)-MRSA were analyzed. The t test and Wilcoxon rank sum test were used for statistical analysis of the quantitative data and Chi-square test were used for comparison of rates. Results: Among the 452 patients, 264 were males and 188 were females, aged from 2 days to 17 years. There were 233 cases (51.5%) in the ≤1 year old group, 79 cases (17.5%) in the>1-3 years old group, 29 cases (6.4%) in the >3-5 years old group, 65 cases (14.4%) in the >5-10 years old group, and 46 cases (10.2%) in the>10 years old group. The main distributions of onset seasons were 55 cases (12.2%) in December, 47 cases (10.4%) in February, 46 cases (10.2%) in November, 45 cases (10.0%) in January, 40 cases (8.8%) in March. There were 335 cases (74.1%) CA-MRSA and 117 (25.9%) cases HA-MRSA. Among all cases, 174 cases (38.5%) had basic diseases or long-term use of hormone and immunosuppressive drugs. During the period of hospitalization, 209 cases (46.2%) received medical interventions. There were 182 patients (40.3%) had used antibiotics (ß-lactams, glycopeptides, macrolides, carbapenems, oxazolones, sulfonamides etc) 3 months before admission. The most common clinical disease was pneumonia (203 cases), followed by skin soft-tissue infection (133 cases), sepsis (92 cases), deep tissue abscess (42 cases), osteomyelitis (40 cases), and septic arthritis (26 cases), suppurative meningitis (10 cases). The proportion of pneumonia in the ≤1 year old group was higher than the >1-3 years old group,>3-5 years old group,>5-10 years old group,>10 years old group (57.5% (134/233) vs. 30.4% (24/79), 31.0% (9/29), 38.5% (25/65), 23.9% (11/46), χ(2)=17.374, 7.293, 7.410, 17.373, all P<0.01) The proportion of skin and soft tissue infections caused by CA-MRSA infection was higher than HA-MRSA (33.4% (112/335) vs. 17.9% (21/117), χ(2)=10.010, P=0.002), and the proportion of pneumonia caused by HA-MRSA infection was higher than CA-MRSA (53.0% (62/117) vs. 42.1% (141/335), χ(2)=4.166, P=0.041). The first white blood cell count of the ≤1 year old group was higher than that children > 1 year old ((15±8)×10(9)/L vs. (13±7)×10(9)/L, t=2.697, P=0.007), while the C-reactive protein of the ≤1 year old group was lower than the 1-3 years old group,>5-10 years old group,>10 years old group (8.00 (0.04-194.00) vs.17.00 (0.50-316.00), 15.20 (0.23-312.00), 21.79(0.13-219.00) mg/L, Z=3.207, 2.044, 2.513, all P<0.05), there were no significant differences in procalcitonin (PCT) between different age groups (all P>0.05). After the treatment, 131 cases were cured, 278 cases were improved, 21 cases were not cured, 12 cases died, and 10 cases were abandoned. The 452 MRSA isolates were all sensitive to vancomycin (100.0%), linezolid (100.0%), 100.0% resistant to penicillin, highly resistant to erythromycin (85.0%, 375/441), clindamycin (67.7%, 294/434), less resistant to sulfonamides (5.9%, 23/391), levofloxacin (4.5%, 19/423), gentamicin (3.2%, 14/438), rifampicin (1.8%, 8/440), minocycline (1.1%, 1/91). The antimicrobial resistance rates were not significantly different between the CA-MRSA and HA-MRSA groups (all P>0.05). Conclusions: The infection of MRSA is mainly found in infants under 3 years old. The prevalent seasons are winter and spring, and MRSA is mainly acquired in the community. The main clinical diseases are pneumonia, skin soft-tissue infection and sepsis. No MRSA isolate is resistant to vancomycin, linezolid. MRSA isolates are generally sensitive to sulfonamides, levofloxacin, gentamicin, rifampicin, minocycline, and were highly resistant to erythromycin and clindamycin. To achieve better prognosis. clinicians should initiate anti-infective treatment for children with MRSA infection according to the clinical characteristics of patients and drug sensitivity of the isolates timely and effectively.

[Guidelines for the use of post-traumatic tetanus vaccines and passive immune preparation].

Post-traumatic tetanus is the main type of non-neonatal tetanus. To reduce the incidence and mortality rateof tetanus and guide the primary medical institutions to prevent and control tetanus after trauma, the National Immunization Planning Technical Working Group of the Chinese Center for Disease Control and Prevention has compiled this document in the reference with Position Paper by World Health Organization, and the latest research progress both at home and abroad. The guidelines focus on the basic procedures for the prevention and treatment of post-traumatic tetanus, the application of tetanus vaccines and immune preparation, and pre-exposure immunization in high-risk populations of trauma.

[Guidelines for the use of post-traumatic tetanus vaccines and passive immune preparation].

Post-traumatic tetanus is the main type of non-neonatal tetanus. To reduce the incidence and mortality rate of tetanus and guide the primary medical institutions to prevent and control tetanus after trauma, National Immunization Planning Technical Working Group of the Chinese Center for Disease Control and Prevention has compiled this document in the reference with Position Paper by World Health Organization, the latest research progress from home and abroad. The guidelines focus on the basic procedures for the prevention and disposition of post-traumatic tetanus, the application of tetanus vaccines and immune preparation, and the pre-exposure immunization in high-risk populations of trauma.

[A multicentric clinical study on clinical characteristics and drug sensitivity of children with pneumococcal meningitis in China].

Objective: To understand clinical characteristics of children with pneumococcal meningitis (PM) in China and to analyze the drug sensitivity of Streptococcus pneumoniae isolates and associated impacts on death and sequelae. Methods: The clinical data, follow-up results and antimicrobial sensitivity of isolated strains of 155 children (including 98 males and 57 females, age ranged from 2 months to 15 years) with PM in 10 tertiary-grade A class hospitals of Infectious Diseases Surveillance of Pediatrics (ISPED) from 2013 to 2017 were collected and analyzed retrospectively. Patients were divided into different groups according to the following standards: ≤1 year old group,>1-3 years old group and >3 years old group according to age; death group and non-death group according to the death within 30 days after PM diagnosis; complication group and non-complication group according to the abnormal cranial imaging diagnosis; sequelae group and no-sequelae group according to the follow-up results. Bonfereoni chi-square segmentation and Kruskal-Wallis H test were used for statistical analysis. Results: There were 64 cases (41.3%) in the ≤1 year old group, 39 cases in the >1-3 years old group (25.2%), and 52 cases (33.5%) in the >3 years old group. The most common clinical manifestation was fever (151 cases, 97.4%). The mortality was 16.8% (26/155) during hospitalization. The neurological complication rate was 49.7% (77/155) during hospitalization, including the most common complication, subdural effusion and (or) empyema in 50 cases (32.3%) and hearing impairment in 6 cases. During follow-up after discharge, no death was found and focal neurological deficits were found in 47 cases (30.3%), including the frequent neurological sequelae: cognitive and mental retardation of different degree in 22 cases and hearing impairment in 14 cases (9.0%). The rate of cure and improvement on discharge was 74.8% (116/155) and the lost to follow-up rate was 8.4% (13/155). The proportions of died cases, neurological complications during hospitalization and proportions of peripheral white blood cell count <12 × 10(9)/L before admission in ≤1 year old group were significantly higher than those in >3 years old group (25.0% (16/64) vs. 5.8% (3/52), 75.0% (48/64) vs. 25.0% (13/52), 48.4% (31/64) vs. 15.4% (8/52), χ(2)=7.747, 28.767, 14.044; P=0.005, 0.000, 0.000). The proportions of headache, vomiting, neck resistance and high risk factors of purulent meningitis in >3 years old group were significantly higher than those in ≤ 1 year old group (67.3%(35/52) vs. 1.6%(1/64), 80.8% (42/52) vs. 48.4% (31/64), 69.2% (36/52) vs. 37.5% (24/64), 55.8% (29/52) vs. 14.1%(9/64), χ(2)=57.940, 12.856, 11.568, 22.656; P=0.000, 0.000, 0.001, 0.000). Streptococcus pneumoniae isolates were completely sensitive to vancomycin (100.0%, 152/152), linezolid (100.0%, 126/126), moxifloxacin (100.0%, 93/93) and ofloxacin (100.0%,41/41); highly sensitive to levofloxacin (99.3%, 142/143) and ertapenem (84.6%, 66/78); moderately sensitive to ceftriaxone (48.4%, 45/93), cefotaxime (40.0%, 44/110) and meropenem (38.0%, 38/100); less sensitive to penicillin (19.6%, 27/138) and erythromycin (4.2%, 5/120). The proportions of non-sensitive strains of penicillin (21/21) and meropenem (17/18) in the death group were significantly higher than those (90/117, 45/82) in the survived group(χ(2)=4.648 and 9.808, P=0.031 and 0.002). Conclusions: The children's PM is mainly found in infants under 3 years old in China. Death and neurological complications are more common in PM children under 1 year old. The clinical manifestations and peripheral blood inflammatory markers of PM patients under 1 year old are not typical. Fever is the most common clinical manifestation and subdural effusion and (or) empyema is the most common complication. Long-term hearing impairment is common in PM and the follow-up time must be prolonged. The dead PM cases had high in sensitive rates to penicillin and meropenem.

[A multicenter clinical study on 1 138 cases of invasive pneumococcal disease in children from 2012 to 2017].

Objective: To explore the clinical features, the serotype distribution and drug resistance of the isolates in patient with invasive pneumococcal disease (IPD). Methods: By retrieving the laboratory information system in 18 children's hospitals from 2012 to 2017, the children with IPD were enrolled. Streptococcus pneumoniae (Spn) must be isolated from the sterile sites (blood, cerebrospinal fluid, hydrothorax and joint effusion etc.). The clinical characteristics, serotype, drug resistance, treatment and prognosis were reviewed and analyzed. According to the telephone follow up results, the patients were divided into death group and recovered group. The index as an independent risk factor of mortality was demonstrated by multivariate logistic regression analysis. Results: There were 1 138 children with IPD, including 684 male and 454 female. The proportion of male to female was 1.5∶1. The age ranged from one day to 16 years. The median age was 1 year 3 month. The majority was under 5 years of age (89.3%, n= 1 016), especially under 2 years of age (61.9%, n=704). In all cases, 88.2% (n=1 004) were community acquired infection. The infections included meningitis (n=446, 39.2%), pneumonia with bacteremia (n=339, 29.8%), and bacteremia without focus (n=232, 20.4%). Underlying diseases were found in 242 cases (21.3%). Co-infections were determined in 62 cases (5.4%) with mycoplasma, 27 cases (2.4%) with adenovirus and 34 cases with influenza virus (3.0%). The penicillin insensitivity (PNSP) rates in meningitis and non-meningitis isolates were 69.5% (276/397) and 35.9% (221/615), respectively. There were 81 strains serotyped, in which 93.8% (76/81) were covered by 13-valent protein-polysaccharide conjugate vaccine (PCV13). In the 965 patients who were followed up by phone call, 156 cases (16.2%) were confirmed dead. The independent risk factors for the death were under 2 years of age (OR=2.143, 95%CI 1.284-3.577, P=0.004), meningitis (OR=3.066, 95%CI 1.852-5.074, P<0.01), underlying disease (OR=4.801, 95%CI 2.953-7.804, P<0.01), septic shock(OR=3.542, 95%CI 1.829-6.859, P<0.01), disseminated intravascular coagulation (DIC) (OR=4.150, 95%CI 1.468-11.733, P=0.007), multiple organ failure (OR=12.693, 95%CI 6.623-24.325, P<0.01) and complications of central nervous system (OR=1.975, 95%CI 1.144-3.410, P=0.015). Conclusions: Most children with IPD were under 5 years of age, having underlying diseases and acquired the infection in community. The independent risk factors for death were under two years old, meningitis, underlying diseases and multiple organ failure. The problem of drug resistance was severe. The universal immunization of PCV13 would be effective to prevent IPD in Chinese children.

[Clinical analysis of 309 hospitalized children with pertussis-associated pneumonia].

Objective: To investigate the clinical characteristics of pertussis-associated pneumonia and analyze it's risk factors. Methods: Clinical data were taken from Shenzhen Children's Hospital with Bordetella pertussis infection and confirmed by culture or real-time polymerase chain reaction (PCR) of nasopharyngeal secretion from October 2013 to December 2015. Patients were divided into two groups, those with radiologically confirmed pneumonia in the course of their disease and those with not. Clinical data were retrospectively analyzed and compared. T test, Rank sum test or chi square test were used for comparison between groups. Risk factors were analyzed by unconditional Logistic regression analysis. Results: A total of 501 children hospitalized with Bordetella pertussis infection were included. Among them, 309 patients were diagnosed with pneumonia. The median age was 3 (2, 6) months. Symptoms were paroxysmal cough (n=252, 81.6%), tachypnea (n=69, 22.3%), and cyanosis (n=105, 34.0%). The time from onset of cough to radiologically confirmed pneumonia was between 1 and 66 days with a median of 9 (5.5, 15.0) days. The most common pathogen of coinfection was respiratory syncytial virus (RSV)(20 cases). Macrolides were used in 306 cases for (8.2±3.6) days. All cases showed significant improvement. There were more male children (62.1% (192/309) vs. 50.3% (95/189) , χ(2)=6.768, P=0.009), and more instances of comorbidities (13.3% (41/309) vs.5.8% (11/189) , χ(2)=6.957, P=0.008) in the pneumonia group than in the other. The age was younger (3 (2,6) vs.4 (2,6) months, Z=32.91, P=0.000) in pneumonia group than in the other. Male sex, younger age, and underlying disease were independent risk factors for pertussis-associated pneumonia (OR=1.648, 1.486, 2.695, P=0.008, 0.036, 0.005). Conclusions: Pneumonia, as a complication of pertussis, is very easy to see in hospitalized children. The duration of hospitalization is extensive. It is more likely to happen in children who are male, young, and having underlying diseases. Pneumonia is easy to occur in the first 2 weeks of the course of disease.

[Clinical characteristics and antimicrobial resistance of pneumococcal infections from 9 children's hospitals in 2016].

Objective: To describe the clinical characteristics of pneumococcal infections and drug resistance of Streptococcus pneumoniae isolates from children's hospitals, which would provide reference for preventing and treating pneumococcal diseases. Methods: This was a prevalence survey. In this study, the age, specimen type, monthly distribution characteristics, and antimicrobial resistance of Streptococcus pneumoniae isolates from 9 children's hospitals in China were investigated between January 1, 2016 and December 31, 2016. The WHONET 5.6 software was used to analyze the antibiotic susceptibility of Streptococcus pneumoniae. The comparison of rates was performed by Chi-square test. Results: A total of 6 200 isolates of streptococcus pneumoniae were obtained, namely, 95.1% (5 876/6 177) from the respiratory tract specimens, 2.2% (136/6 177) from blood specimens and 0.4% (24/6 177) from cerebrospinal fluid specimens. The isolates were mainly from children older than 1 and younger than 5 years (54.7%, 3 381/6 185) . Most of strains (33.2%, 1 184/3 563) were isolated in November, December and January. Streptococcus pneumoniae isolates were completely sensitive to vancomycin (100.0%, 6 189/6 189) , linezolid (100.0%, 6 030/6 030) , moxifloxacin (100.0%, 3 064/3 064) , highly sensitive to levofloxacin (99.8%, 5 528/5 540), ertapenem (98.8%, 3 024/3 061) and lowly sensitive to erythromycin (1.7%, 102/6 016), clindamycin (3.7%, 116/3 136), and tetracycline (5%, 244/4 877), respectively. According to the parenteral susceptibility breakpoints for non-meningitis isolates, the sensitivity of Streptocococus pneumoniae to penicillin from children's hospital of Chongqing Medical University (49.3%, 892/1 809) was significantly lower than those of other hospitals (χ(2)=1 268.161, P<0.05) . Conclusions:Streptococcus pneumoniae is mainly isolated from respiratory tract, from children older than 1 and younger than 5 years and during November to January in tertiary children's hospital of China. The Streptococcus pneumoniae from children is highly sensitive to vancomycin, linezolid, moxifloxacin, levofloxacin. There are also significant differences in the sensitivity of penicillin for Streptococcus pneumoniae from different hospitals.

[Report of antimicrobial resistance surveillance program in Chinese children in 2016].

Objective: To analyze the antimicrobial resistance profile in Chinese children. Methods: This was a prevalence survey. From January 1 through December 31, 2016, the isolates were collected from 10 tertiary children hospitals in China. Antimicrobial susceptibility testing was carried out by routine laboratory methods. The penicillin susceptibility of streptococcus pneumonia and Meropenem susceptibility of gram-negative bacteria were detected by E-test and disk diffusion method respectively. Antimicrobial susceptibility results were interpreted according to the criteria of Clinical and Laboratory Standards Institute (CLSI) Guideline 2016. The data of antimicrobial susceptibility testing of isolates from either the different patients (neonatal group and non-neonatal group) or various sources were analyzed by WHONET 5.6 software. Results: A total of 56 241 isolates were collected, of which 41.5% (23 328 isolates) were gram-positive organisms and 58.5% (32 886 isolates) gram-negative organisms. The five leading pathogens were Escherichia coli (7 995/56 214, 14.2%), Straphylococcus aureus (6 468/56 214, 11.5%), Streptococcus pneumonia (6 225/56 214, 11.1%), Haemophilus influenza (5 435/56 214, 9.7%) and Klebsiella pneumonia (4 523/56 214, 8.0%). The Meropenem resistance rates of Klebsiella pneumonia, Enterobacter cloacae, Escherichia coil, Pseudomonas aeruginosa, Acinetobacter baumonia isolates were 27.4% (326/1 189) , 8.1% (29/358) , 2.0% (27/1 362) , 19.5% (34/174) , 49.7% (230/463) in neonatal group and 15.4% (512/3 327) , 4.8% (40/841) , 2.3% (151/6 564) , 13.7% (252/1 840) , and 53.4% (860/1 611) in non-neonatal group. The Methicillin-resistant Staphylococcus aureus (MRSA) rates of neonatal group and non-neonatal group were 46.2% (649/1 404) and 33.3% (1 668/5 010) . The penicillin non-susceptible rates of Streptococcus pneumonia in the two groups were 17.6% (6/34) and 18.2% (1 121/6 158) respectively. The ß-lactamase positive rates of Haemophilus pneumonia isolates in the neonatal group and non-neonatal groups were 33.8% (47/139) and 44.4% (2 345/5 282) respectively. Conclusion: This investigation highlights the worrisome trend of antimicrobial resistance in children, especially among neonatal patients in China.

The Jahn-Teller effect in the electron momentum spectroscopy of ammonia.

The 1e and 3a(1) bands of the ammonia molecule have been studied using the high-resolution electron momentum spectroscopy at impact energies of 1200 and 600 eV. Several slices of 1e and 3a(1) bands in the different binding energy ranges were selected, and their electron-momentum distributions were carefully compared. The discernable difference among the distributions of the selected slices of the 1e band shows that the Jahn-Teller effect indeed influences the electron momentum distribution of the 1e orbital of ammonia.

Vibrational effects on the electron momentum distributions of valence orbitals of formamide.

The ionization energy spectra and electron momentum distributions of formamide were investigated using the high-resolution electron momentum spectrometer in combination with high level calculations. The observed ionization energy spectra and electron momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a(') and 2a(") orbitals of formamide was assigned unambiguously by comparing the experimental electron momentum distributions with the corresponding theoretical results, i.e., 10a(') has a lower binding energy. In addition, it was found that the low-frequency wagging vibration of the amino group at room temperature has noticeable effects on the electron momentum distributions. The equilibrium-nuclear-positions-approximation, which was widely used in electron momentum spectroscopy, is not accurate for formamide molecule. The calculations based on the thermal average can evidently improve the agreement with the experimental momentum distributions.

Dyson orbitals of N2O: electron momentum spectroscopy and symmetry adapted cluster-configuration interaction calculations.

Electron momentum spectroscopy and symmetry adapted cluster-configuration interaction (SAC-CI) theory were combined to study electron correlation effects in nitrous oxide molecule (N(2)O). The SAC-CI General-R method accurately reproduced the experimental ionization spectrum. This bench-marked method was also introduced for calculating the momentum distributions of N(2)O Dyson orbitals. Several calculated momentum distributions with different theoretical methods were compared with the high resolution experimental results. In the outer-valence region, Hartree-Fock (HF), density functional theory (DFT), and SAC-CI theory can well describe the experimental momentum distributions. SAC-CI presented a best performance among them. In the inner-valence region, HF and DFT cannot work well due to the severe breaking of the molecular orbital picture, while SAC-CI still produced an excellent description of experimental momentum profiles because it can accurately take into account electron correlations. Moreover, the thermally averaged calculation showed that the geometrical changes induced by the vibration at room temperature have no noticeable effects on momentum distribution of valence orbitals of N(2)O.

Experimental and theoretical electron momentum spectroscopic study of the valence electronic structure of tetrahydrofuran under pseudorotation.

The most populated structure of tetrahydrofuran (THF) has been investigated in our previous study using electron momentum spectroscopy (EMS). Because of the relatively low impact energy (600 eV) and low energy resolution (DeltaE = 1.20 eV) in the previous experiment, only the highest occupied molecular orbital (HOMO) of THF was investigated. The present study reports the most recent high-resolution EMS of THF in the valence space for the first time. The binding energy spectra of THF are measured at 1200 and 2400 eV plus the binding energies, respectively, for a series of azimuthal angles. The experimentally obtained binding energy spectra and orbital momentum distributions (MDs) are employed to study the orbital responses of the pseudorotation motion of THF. The outer valence Greens function (OVGF), the OVGF/6-311++G** model, and density function theory (DFT)-based SAOP/et-pVQZ model are employed to simulate the binding energy spectra. The orbital momentum distributions (MDs) are produced using the DFT-based B3LYP/aug-cc-pVTZ model, incorporating thermodynamic population analysis. Good agreement between theory and experiment is achieved. Orbital MDs of valence orbitals exhibit only slight differences with respect to the impact energies at 1200 and 2400 eV, indicating validation of the plane wave impulse approximation (PWIA). The present study has further discovered that the orbital MDs of the HOMO in the low-momentum region (p < 0.70 a.u) change significantly with the pseudorotation angle, phi, giving a v-shaped cross section, whereas the innermost valence orbital of THF does not vary with pseudorotation, revealing a very different bonding mechanism from the HOMO. The present study explores an innovative approach to study pseudorotation of sugar puckering, which sheds a light to study other biological systems with low energy barriers among ring-puckering conformations.

Study of the valence wave function of thiophene with high resolution electron momentum spectroscopy and advanced Dyson orbital theories.

Results of an exhaustive experimental study of the valence electronic structure of thiophene using high resolution electron momentum spectroscopy at impact energies of 1200 and 2400 eV are presented. The measurements were performed using an electron momentum spectrometer of the third generation at Tsinghua University, which enables energy, polar and azimuthal angular resolutions of the order of DeltaE = 0.8 eV, Deltatheta = +/-0.53 degrees and Deltaphi = +/-0.84 degrees . These measurements were interpreted by comparison with Green's function calculations of one-electron and shake-up ionization energies as well as of the related Dyson orbital electron momentum distributions, using the so-called third-order algebraic diagrammatic construction scheme (ADC(3)). Comparison of spherically averaged theoretical electron momentum distributions with experimental results very convincingly confirms the presence of two rather intense pi-2 pi*+1 shake-up lines at electron binding energies of 13.8 and 15.5 eV, with pole strengths equal to 0.18 and 0.13, respectively. Analysis of the electron momentum distributions associated with the two lowest 2A2 (pi3-1) and 2B1 (pi2-1) cationic states provides indirect evidence for a symmetry lowering and nuclear dynamical effects due to vibronic coupling interactions between these two states. ADC(3) Dyson orbital momentum distributions are systematically compared with distributions derived from Kohn-Sham (B3LYP) orbitals, and found to provide most generally superior insights into experiment.

Probing molecular conformations in momentum space: the case of n-pentane.

A comprehensive study, throughout the valence region, of the electronic structure and electron momentum density distributions of the four conformational isomers of n-pentane is presented. Theoretical (e,2e) valence ionization spectra at high electron impact energies (1200 eV+electron binding energy) and at azimuthal angles ranging from 0 degrees to 10 degrees in a noncoplanar symmetric kinematical setup are generated according to the results of large scale one-particle Green's function calculations of Dyson orbitals and related electron binding energies, using the third-order algebraic-diagrammatic construction [ADC(3)] scheme. The results of a focal point analysis (FPA) of relative conformer energies [A. Salam and M. S. Deleuze, J. Chem. Phys. 116, 1296 (2002)] and improved thermodynamical calculations accounting for hindered rotations are also employed in order to quantitatively evaluate the abundance of each conformer in the gas phase at room temperature and reliably predict the outcome of experiments on n-pentane employing high resolution electron momentum spectroscopy. Comparison with available photoelectron measurements confirms the suggestion that, due to entropy effects, the trans-gauche (tg) conformer strongly dominates the conformational mixture characterizing n-pentane at room temperature. Our simulations demonstrate therefore that experimental measurements of (e,2e) valence ionization spectra and electron momentum distributions would very consistently and straightforwardly image the topological changes and energy variations that molecular orbitals undergo due to torsion of the carbon backbone. The strongest fingerprints for the most stable conformer (tt) are found for the electron momentum distributions associated with ionization channels at the top of the inner-valence region, which sensitively image the development of methylenic hyperconjugation in all-staggered n-alkane chains.

Imaging momentum orbital densities of conformationally versatile molecules: a benchmark theoretical study of the molecular and electronic structures of dimethoxymethane.

The main purpose of the present work is to predict from benchmark many-body quantum mechanical calculations the results of experimental studies of the valence electronic structure of dimethoxymethane employing electron momentum spectroscopy, and to establish once and for all the guidelines that should systematically be followed in order to reliably interpret the results of such experiments on conformationally versatile molecules. In a first step, accurate calculations of the energy differences between stationary points on the potential energy surface of this molecule are performed using Hartree-Fock (HF) theory and post-HF treatments of improving quality (MP2, MP3, CCSD, CCSD(T), along with basis sets of increasing size. This study focuses on the four conformers of this molecule, namely the trans-trans (TT), trans-gauche (TG), gauche-gauche (G+G+), and gauche-gauche (G+G-) structures, belonging to the C2v, C1, C2, and Cs symmetry point groups, respectively. A focal point analysis supplemented by suited extrapolations to the limit of asymptotically complete basis sets is carried out to determine how the conformational energy differences at 0 K approach the full CI limit. In a second step, statistical thermodynamics accounting for hindered rotations is used to calculate Gibbs free energy corrections to the above energy differences, and to evaluate the abundance of each conformer in the gas phase. It is found that, at room temperature, the G+G+ species accounts for 96% of the conformational mixture characterizing dimethoxymethane. In a third step, the valence one-electron and shake-up ionization spectrum of dimethoxymethane is analyzed according to calculations on the G+G+ conformer alone by means of one-particle Green's function [1p-GF] theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. A complete breakdown of the orbital picture of ionization is noted at electron binding energies above 22 eV. A comparison with available (e,2e) ionization spectra enables us to identify specific fingerprints of through-space orbital interactions associated with the anomeric effect. At last, based on our 1p-GF/ADC(3) assignment of spectral bands, accurate and spherically averaged (e,2e) electron momentum distributions at an electron impact energy of 1200 eV are computed from the related Dyson orbitals. Very significant discrepancies are observed with momentum distributions obtained for several outer-valence levels using standard Kohn-Sham orbitals.

Investigation of valence orbitals of propene by electron momentum spectroscopy.

The binding energy spectra and momentum distributions of all valence orbitals of propene were studied by electron momentum spectroscopy (EMS) as well as Hartree-Fock and density functional theoretical calculations. The experiment was carried out at impact energies of 1200 eV and 600 eV on the state-of-the-art EMS spectrometer developed at Tsinghua University recently. The experimental momentum profiles of the valence orbitals were obtained and compared with the various theoretical calculations. Moreover, the experiment with a new analysis method presents a strong support for the correct ordering of the orbital 8a' and 1a'', i.e., 9a' < 8a' < 1a'' < 7a'.

Direct observation of distorted wave effects in ethylene using the (e,2e) reaction.

We report here the direct measurements of electron momentum distributions for ethylene using the (e,2e) reaction at different impact energies from 400 to 2400 eV. The "turn up" effects in the (e,2e) cross sections of the 1b(3g) orbital compared with the plane-wave impulse approximation calculations were observed at low and high momentum regions, and such discrepancies become smaller with the increase of the impact electron energies. It is suggested that the observed discrepancies are due to the distorted-wave effects in molecules, while appropriate theoretical calculations using distorted waves in molecules could not be achieved until now.