Novel ratiometric electrochemical aptasensor based on broad-spectrum aptamer recognition for simultaneous detection of penicillin antibiotics in milk.

To effectively monitor multi-residues of penicillin antibiotics (PENs) in milk, we developed a novel ratiometric electrochemical aptasensor enabling simultaneous detection of PENs. The aptasensor employed a broad-spectrum aptamer as a recognition element, niobium carbide functionalized with methylene blue (Nb2C-MB) as a reference signal generator, and a ferrocene-labeled aptamer (Fc-Apt) as an output signal. Electrodes were modified with Fe-N-C doped carbon nanotubes (Fe-N-C-CNTs) to amplify detection signals further. During detection, Fc-Apt binding to PENs decreased Fc current intensity (IFc) and increased MB current intensity (IMB). The simultaneous detection of PENs was achieved using IMB/IFc as a quantitative signal. Under optimal conditions, a good linear relationship between IMB/IFc and antibiotic concentration was observed, indicating the aptasensor had a robustness. The limits of detection of aptasensor for four penicillin antibiotics and their mixed targets were 0.093-0.191 nM. This work provides a new approach to multi-residue detection of the same class of antibiotics.

Screening of broad-spectrum aptamer and development of electrochemical aptasensor for simultaneous detection of penicillin antibiotics in milk.

Penicillin antibiotics (PENs) play an important role in killing pathogenic bacteria. However, the residues of various penicillin antibiotics in milk gradually accumulate in the human body with the increase of milk intake, which causes direct harm to the human body. Aptamers can be used as recognition element of sensors. It is great significance to use broad-spectrum aptamers for simultaneous detection of PENs. In this study, we reported the screening and identification of DNA aptamers for PENs. The aptamers were screened by graphene oxide-systematic evolution of ligands by exponential enrichment (GO-SELEX). The broad-spectrum aptamers with high affinity and specificity were successfully obtained after 13 rounds of screening. The affinity and specificity of candidate aptamers were analyzed by a GO fluorescence competition method. Further sequence analysis revealed that a truncated 47 nt aptamer (P-11-1) had a higher affinity than the original 79 nt aptamer. The truncated aptamer P-11-1 was used as a recognition element, and an electrochemical aptasensor was prepared using gold nanoparticles (AuNPs) combined with ferroferric oxide-multi walled carbon nanotube (Fe3O4-MWCNTs) complex. The results showed that the developed aptasensor achieved the simultaneous detection of PENs in milk samples across a concentration range of 2 nM-10,000 nM, achieving a limit of detection of 0.667 nM. This methodology provided a simple and sensitive new thinking for antibiotic multi-residue detection.

Clinical significance of CT angiographic assessment of collateral circulation combined with serum NLRP1 levels in ischemic stroke patients.

This research aimed to combine serum NLR-pyrin domain containing 1 (NLRP1) levels and collateral circulation to assess ischemic stroke patients and predict the prognoses of the patients. This present prospective observational study enrolled 196 ischemic stroke patients. All patients underwent CTA as well as digital subtraction angiography (DSA) to assess collateral circulation by American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR). In addition, we collected serum samples from 100 patients with carotid atherosclerosis as controls. The serum NLRP1, tumor necrosis factor α (TNF-α), interleukin (IL)-6, IL-1ß and C-reactive protein (CRP) levels were measured by enzyme-linked immunosorbent assay (ELISA). The age, BMI, sex, smoke condition, diastolic blood pressure, systolic blood pressure, National Institutes of Health Stroke Scores (NIHSS), modified Rankin Scale (mRS) scores, imaging indicators and the levels of triglyceride, total cholesterol (TC), low-density leptin cholesterol (LDLC), high-density leptin cholesterol of all subjects were recorded. All data used SPSS 18.0 to statistical analyses. The serum levels of NLRP1 were remarkably enhanced in the ischemic stroke patients compared with the carotid atherosclerosis patients. The NIHSS score, the mRS score after 90 days and the levels of NLRP1, CRP, TNF-α IL-6 and IL-1ß of ischemic stroke patients in the ASITN/SIR grade 0 to 2 group were remarkably elevated than the ischemic stroke patients in ASITN/SIR grade 3 to 4 group. Spearman analysis supported that a positive correlation existed among the NLRP1, CRP, IL-6, TNF-α, and IL-1ß levels. The NIHSS score, infarct volume and the levels of NLRP1, IL-6, TNF-α, and IL-1ß of ischemic stroke patients in the mRS score ≥ 3 group were remarkably elevated than the ischemic stroke patients in the mRS score ≤ 2 group. ASITN/SIR grade and NLRP1 could be potential diagnostic biomarkers of poor prognosis of ischemic stroke patients. It was found that NLRP1, ASITN/SIR grade, infarct volume, NIHSS, IL-6, and IL-1ß were the risk factors for bad prognosis of ischemic stroke patients. This study showed that the serum NLRP1 levels were remarkably decreased in ischemic stroke patients. In addition, the serum NLRP1 levels and ASITN/SIR grade could predict the prognosis of ischemic stroke patients.

Meta-analysis of therapeutic efficacy and effects of integrated traditional Chinese and Western medicine on coagulation and fibrinolysis system in patients with threatened abortion and polycystic ovary syndrome.

BACKGROUND: Polycystic ovary syndrome (PCOS) patients are prone to early pregnancy loss. Studies have found that the blood fibrinolytic activity of PCOS patients is closely related to the high abortion rate. At present, it is considered that the combination of traditional Chinese and Western medicine in the treatment of PCOS with threatened abortion has a good effect on fetal protection. Therefore, the clinical efficacy of the combination of traditional Chinese and Western medicine in the treatment of PCOS with threatened abortion was systematically evaluated, and the effect of traditional Chinese medicine on the blood fibrinolytic status of patients was also evaluated. METHODS: The clinical randomized controlled trials (RCTs) of integrated traditional Chinese and Western medicine in the treatment of PCOS with threatened abortion were reviewed from four Chinese databases (CNKI, WANFANG, VIP, and SINOMED) and two English databases (PubMed, EMBASE) from their time of establishment to May 2021. According to the inclusive and exclusive criteria, tests were selected, data were extracted and evaluated, the systematic review was carried out by description analysis, and the meta-analysis was conducted using RevMan 5.3 software from Cochrane Collaboration. Begg's and Egger's tests were performed for assessing symmetries of funnel plot by the software Stata 16.0. RESULTS: 6 RCTs involving 361 participants were included. Meta-analysis results showed that integrated traditional Chinese and Western medicine can increase the total efficacy compared with the control groups [RR=1.22, 95% CI (1.10, 1.35), P=0.0002]. Meanwhile, the improvement of TCM syndrome integral [MD=-2.11, 95% CI (-2.56, -1.66), P<0.00001], D-II [MD=-0.29, 95% CI (-0.49, -0.09), P=0.004], Hcy [MD=-3.02, 95% CI (-3.64, -2.39, P=0.00001], PAI-I [SMD=-2.38, 95% CI (-2.82, -1.73), P<0.00001] were better than a single Western medicine treatment. And it can increase the level of ß-HCG [SMD=3.44, 95% CI (1.87, 5.01), P<0.0001], P [MD=7.70, 95% CI (7.10, 8.31), P<0.00001], E2 [MD=205.36, 95% CI (140.93, 269.80), P<0.00001]. The funnel plot, Egger's test (P=0.210), and Begge's test (P=0.573) suggested that there was no evidence of substantial publication bias. CONCLUSIONS: The effect of integrated traditional Chinese and Western medicine is better than that of Western medicine alone in the treatment of PCOS with threatened abortion, and it has certain advantages in improving the fibrinolytic status of patients. However, due to the limitation of the quality and quantity of the included literature, more rigorous and larger sample studies are needed to confirm these conclusions in the future.

Spectroscopy and dynamics of the predissociated, quasi-linear S2 state of chlorocarbene.

In this work, we report on the spectroscopy and dynamics of the quasi-linear S(2) state of chlorocarbene, CHCl, and its deuterated isotopologue using optical-optical double resonance (OODR) spectroscopy through selected rovibronic levels of the S(1) state. This study, which represents the first observation of the S(2) state in CHCl, builds upon our recent examination of the corresponding state in CHF, where pronounced mode specificity was observed in the dynamics, with predissociation rates larger for levels containing bending excitation. In the present work, a total of 14 S(2) state vibrational levels with angular momentum l = 1 were observed for CHCl, and 34 levels for CDCl. The range of l in this case was restricted by the pronounced Renner-Teller effect in the low-lying S(1) levels, which severely reduces the fluorescence lifetime for levels with K(a) > 0. Nonetheless, by exploiting different intermediate S(1) levels, we observed progressions involving all three fundamental vibrations. For levels with long predissociation lifetimes, rotational constants were determined by measuring spectra through different intermediate J levels of the S(1) state. Plots of the predissociation linewidth (lifetime) vs. energy for various S(2) levels show an abrupt onset, which lies near the calculated threshold for elimination to form C((3)P) + HCl on the triplet surface. Our experimental results are compared with a series of high level ab initio calculations, which included the use of a dynamically weighted full-valence CASSCF procedure, focusing maximum weight on the state of interest (the singlet and triplet states were computed separately). This was used as the reference for subsequent Davidson-corrected MRCI(+Q) calculations. These calculations reveal the presence of multiple conical intersections in the singlet manifold.

[Mutiple-slice spiral CT diagnosis of atypical intraabdominal hernia].

OBJECTIVE: To discuss the value of multiple-slice spiral CT diagnosis of atypical intraabdominal hernia. METHODS: The clinical and CT findings of 16 cases of atypical intraabdominal hernia confirmed surgically were retrospectively analysed. RESULTS: In all the 16 cases, the contents of hernia were small bowels and the mesentery. Nine cases were caused by the adhesion after abdominal operations or infection, 6 by the mesenteric foramen, and 1 by the gap of pelvic peritoneum. The main CT findings were as follows:(1)the obstructed small bowels gathered abnormally and showed cluster shape(9 cases); the walls of the bowels thickened with edema and showed "target" sign with exudate in the neighboring spaces(5 cases); other part of the abdominal cavity became empty for lack of small bowels(4 cases).(2) Abnormal arrangement of the branches of mesenteric vessel, which appeared gathered or pulled or rigid and displacement of the main branches to left or right(12 cases). Thickened mesenteric vessel (4 cases): torsion of mesentery with "whirlpool" sign (3 cases). (3) With the help of multiplanar reformation, 5 cases showed the evidence of hernia rings. In the ring area, there were gathered or pulled or rigid and radiating mesenteric vessel and the dilated or effusion bowels in cluster arrangement forming "parachute" and "bundle of balloons" sign. CONCLUSION: CT manifestations of atypical intraabdominal hernia has some specific characteristics, which is of important value for clinical diagnosis and treatment.

Optical-optical double resonance spectroscopy of the quasi-linear S2 state of CHF and CDF. I. Spectroscopic analysis.

In this work, we report on our full results of the spectroscopic analysis of the quasi-linear S(2) state of the prototypical halocarbene, CHF, and its deuterated isotopomer CDF using optical-optical double resonance spectroscopy through the S(1) state. A total of 51 S(2) state vibrational levels with angular momenta in the range [script-l] = 0-3 were observed for CHF, and 76 levels for CDF. Progressions involving all three fundamental vibrations were observed, and rotational constants were determined for each of these levels by measuring spectra through different intermediate J levels of the S(1) state. Our experimental results are in excellent agreement with the predictions of vibrational calculations using the discrete variable representation method. The variational vibrational calculations were performed with an analytic potential energy surface fit to ab initio data by the method of interpolating moving least squares. The ab initio data are Davidson-corrected multi-reference configuration interaction calculations based on a state-averaged multiconfigurational self-consistent field reference incorporating a generalized dynamic weighting scheme.

Optical-optical double resonance spectroscopy of the quasi-linear S2 state of CHF and CDF. II. Predissociation and mode-specific dynamics.

In this work, we report on our full results of the dynamics of the quasi-linear, predissociated S(2) state of the prototypical halocarbene, CHF, and its deuterated isotopomer CDF using optical-optical double resonance spectroscopy through the S(1) state. Homogeneous linewidths were determined for a total of 51 S(2) state vibrational levels with angular momenta in the range [script-l] = 0-3 for CHF, and 76 levels for CDF. Progressions involving all three fundamental vibrations were observed. The linewidth data reveal pronounced mode specificity for both CHF and CDF, where pure bending states have the largest linewidths. For CDF, the linewidths are uniformly narrower. Calculated (CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVQZ) stationary points on the CHF potential energy surface show that two dissociative pathways are available at the energies accessed in this experiment: dissociation on the triplet surface, over a barrier, to form C((3)P) + HF, and dissociation to ground state CF + H products. The former is excluded as a primary channel based on the small spin-orbit coupling in this system. A 27-state dynamically weighted full-valence complete active space self-consistent field calculation was performed with maximal weight focused on the S(2) state, which was then used as a reference for Davidson-corrected multireference configuration interaction calculations MRCI(+Q) of the three lowest A(') and two lowest A(") states. These calculations reveal the presence of multiple conical intersections in the singlet manifold. Consistent with our experimental results, the most important of these involves the repulsive S(3) state, which conically intersects with S(2) at linearity.

Primary closure versus T-tube drainage after common bile duct exploration for choledocholithiasis.

PURPOSE: The aim of this study was to evaluate the benefits and harms of primary closure versus T-tube drainage after common bile duct (CBD) exploration for choledocholithiasis. METHODS: A literature search of MEDLINE (PubMed), EMBASE, and the Cochrane Library was done to identify randomized controlled trials assessing the benefits and harms of primary closure versus T-tube drainage after CBD exploration from Jan. 1990 to Apr. 2010. A meta-analysis was set up to distinguish overall difference between the primary closure and the T-tube drainage group. RESULTS: There were statistically significant differences between groups: biliary complications (odds ratio (OR) 95% confidence interval (CI), 0.42 (0.19-0.92); P = 0.03), main complications (OR 95% CI, 0.46 (0.23-0.90); P = 0.02), operating time (weighted mean difference (WMD) 95% CI, -19.53 (-29.35 to -9.71); P < 0.0001), and hospital stay (WMD 95% CI, -4.16 (-7.07 to -1.24); P = 0.005) except peri-operative mortality (OR 95% CI, 0.83 (0.11-6.37); P = 0.86), residual stones (OR 95% CI, 0.70 (0.22-2.25); P = 0.55), and abdominal collections (OR 95% CI, 1.93 (0.34-10.76); P = 0.46). And the result of wound infection (OR 95% CI, 0.38 (0.14-1.02); P = 0.05) tended to favor the primary closure group. CONCLUSION: The primary closure might be as effective as T-tube drainage after choledochotomy in the prevention of the development of post-operative complications.

The effect of splenic arterial blood flow (SBF) on severity of hypersplenism and analysis of factors associated with SBF.

BACKGROUND: This study aims to explore the relationship between spleen arterial blood flow (SBF) with platelet count, spleen index (SPI) and the serum nitric oxide (NO) level of patients with liver cirrhosis and to investigate the role of SBF in the development of hypersplenism. METHODOLOGY: Platelet count, SPI, SBF and serum NO levels were evaluated in 100 patients with liver cirrhosis caused by hepatitis B with hypersplenism (cirrhosis group) and 30 healthy persons without hypersplenism (control group). RESULTS: Platelet count in cirrhosis group and control group was 57.0 +/- 25.6 x 109/L and 205.8 +/- 47.4 x 109/L (p = 0.000), SBF was 535.7 +/- 263.7 milmin and 172.2 +/- 66.9 ml/min (p = 0.000), and serum NO level was 98.51 +/- 23.06 micromol/L and 48.43 +/- 19.47 micromol/L (p = 0.000). Linear correlations were made between SBF and platelet count in cirrhosis group (r = -0.573, p = 0.000), SBF and SPI (r = 0.607, p = 0.01), SBF and serum NO level (r = 0.754, p = 0.000). Moreover, serum NO level increased as liver disease aggravated (82.50 +/- 15.04 pmol/L in Child grade A, 94.61 +/- 21.00 micromol/L in grade B and 116.83 +/- 18.03 micromol/L in grade C; grade A versus grade C, p = 0.003). CONCLUSION: The elevation of SBF may play an important role in the development of hypersplenism and disorders in vasoactive factors such as the serum NO caused by liver cirrhosis may play an important role in the elevation of SBF.

Efficacy of mechanical bowel preparation with polyethylene glycol in prevention of postoperative complications in elective colorectal surgery: a meta-analysis.

PURPOSE: The aim of this study was to estimate efficacy of mechanical bowel preparation with polyethylene glycol (PEG) in prevention of postoperative complications in elective colorectal surgery. METHOD: A literature search of MEDLINE (PubMed), EMBASE, and the Cochrane Library was done to identify randomized controlled trials involving comparison of postoperative complications after mechanical bowel preparation with PEG (PEG group) and no preparation (control group). A meta-analysis was set up to distinguish overall difference between the two groups. RESULTS: A total of five randomized controlled trials was identified according to our inclusion criteria. The use of PEG for mechanical bowel preparation did not significantly reduce the rate of surgical site infection (SSI; odds ratio (OR) 95% confidence interval (CI), 1.39 (0.85-2.25); P = 0.19) including incisional SSI (OR 95% CI, 1.44 (0.88-2.33); P = 0.15), organ/space SSI (OR 95% CI, 1.10 (0.43-2.78); P = 0.49), anastomotic leak (OR 95% CI,1.78 (0.95-3.33; P = 0.07), mortality (OR 95% CI, 1.24 (0.37-4.14; P = 0.73), infectious complications (OR 95% CI, 1.14 (0.62-2.08); P = 0.67), and hospital stay (weighted mean difference 95% CI, 2.17 (-2.90-7.25); P = 0.40) except main complications (OR 95% CI, 1.76 (1.09-2.85); P = 0.02), of which the rate increased significantly in the PEG group. CONCLUSION: The use of mechanical bowel preparation with PEG does not significantly lower postoperative complications in elective colorectal surgery.

Fluorescence excitation and emission spectroscopy of the X(1)A' --> A(1)A'' system of CHI and CDI.

We report on the first detailed studies of the spectroscopy of an iodocarbene, measuring fluorescence excitation and emission spectra of the X1A' --> A1A'' system of :CHI and the deuterated isotopomer :CDI. Due to similar bending and C-I stretching frequencies in the upper state, fluorescence excitation spectra of :CHI show polyads composed of members of the 2(0)(n-x)3(0)x progressions with x = 0-3. For :CDI, only progressions with x = 0, 1 are observed. Extrapolation of the 20n term energies for both isotopomers to a common origin places the electronic origin of the X1A' --> A1A'' system near 10500 cm-1, in good agreement with theoretical predictions. Rotational analysis of the 16 observed bands for CHI and 13 observed bands for :CDI yields rotational constants for the upper and lower states that are also in good agreement with theory. To investigate the controversial issue of the ground state multiplicity of :CHI, we measured single vibronic level emission spectra from many A1A'' levels. These spectra show conclusively that the ground state is a singlet, as for both isotopomers the ã3A'' origin is observed, lying well above the origin of the X1A' state. At energies above the ã3A'' origin, the spin-orbit mixing is so severe that few vibrational assignments can be made. Analysis of the emission spectra provides a lower limit on the singlet-triplet gap of 4.1 kcal mol-1, in excellent agreement with theoretical predictions.

High resolution study of spin-orbit mixing and the singlet-triplet gap in chlorocarbene: stimulated emission pumping spectroscopy of CH(35)Cl and CD(35)Cl.

We report on high resolution studies of spin-orbit mixing and the singlet-triplet gap in a prototypical halocarbene, CHCl, using stimulated emission pumping (SEP) spectroscopy from the A (1)A(") state. Results are reported for two isotopomers, CH(35)Cl and CD(35)Cl. We have obtained rotationally resolved spectra for the majority of X (1)A(') levels lying between 0 and 6000 cm(-1) above the zero-point level that were previously observed under low resolution in single vibronic level emission studies and several new levels that were previously unobserved or unresolved. In addition, SEP spectra were obtained for six a (3)A(") levels in CH(35)Cl and three levels in CD(35)Cl. The derived term energies and rovibrational parameters of the X (1)A(') and a (3)A(") states are in good agreement with theory. The a (3)A(") triplet spin-spin parameter is vibrational state dependent, and dominated by a second-order contribution from spin-orbit coupling with nearby X (1)A(') levels; it therefore provides a sensitive probe of spin-orbit mixing in this system. An analysis of three pairs of interactions between specific a (3)A(") and X (1)A(') levels in CH(35)Cl affords a pure electronic spin-orbit coupling element of 150 cm(-1), in good agreement with theoretical expectations. The derived singlet-triplet gaps, which are the most precise determined to date for any carbene, are compared with the predictions of high level ab initio theory.

First observation of the elusive iodocarbene: ground state multiplicity and singlet-triplet gap of CHI.

We report the first observation of iodocarbene (CHI) using fluorescence excitation and emission spectroscopy, which indicate a singlet ground state and a lower bound to the singlet-triplet gap of 3.76 kcal mol(-1).

Unraveling the A(1)B1 <-- X(1)A1 spectrum of CCl2: The Renner-Teller effect, barrier to linearity, and vibrational analysis using an effective polyad Hamiltonian.

We report studies aimed at unraveling the complicated structure of the CCl 2 A (1)B 1 <-- X (1)A 1 system. We have remeasured the fluorescence excitation spectrum from approximately 17,500 to 24,000 cm (-1) and report the term energies and A rotational constants of many new bands for both major isotopologues (C (35)Cl 2, C (35)Cl (37)Cl). We fit the observed term energies to a polyad effective Hamiltonian model and demonstrate that a single resonance term accounts for much of the observed mixing, which begins approximately 1300 cm (-1) above the vibrationless level of the A (1)B 1 state. The derived A (1)B 1 vibrational parameters are in excellent agreement with ab initio predictions, and the mixing coefficients deduced from the polyad model fit are in close agreement with those derived from direct fits of single vibronic level (SVL) emission intensities. The approach to linearity and thus the Renner-Teller (RT) intersection is probed through the energy dependence of the A rotational constant and fluorescence lifetime measurements, which indicate a barrier height above the vibrationless level of the X (1)A 1 state of approximately 23,000-23,500 cm (-1), in excellent agreement with ab initio theory.

High resolution probe of spin-orbit coupling and the singlet-triplet gap in chlorocarbene.

Among the most important of chemical intermediates are the carbenes, characterized by a divalent carbon that generates low-lying biradical (triplet) and spin-paired (singlet) configurations with unique chemical reactivities. The "holy grail" of carbene chemistry has been determining the singlet-triplet gap and intersystem crossing rates. We report here the first high resolution spectra of singlet-triplet transitions in a prototypical singlet carbene, CHCl, which probe in detail the triplet state structure and spin-orbit coupling with the ground singlet state. Our spectra reveal a pronounced vibrational state dependence of the triplet state spin-spin splitting parameter, which we show is a sensitive probe of spin-orbit coupling with nearby singlet states. The parameters derived from our spectra, including a precise determination of the singlet-triplet energy gap, are in excellent agreement with recent ab initio calculations.

Stimulated emission pumping spectroscopy of the [X](1)A' state of CHF.

We have recorded stimulated emission pumping (SEP) spectra of the A1A' ' 1A' system of CHF, which reveal rich detail concerning the rovibronic structure of the 1A' state up to approximately 7000 cm-1 above the vibrationless level. Using several intermediate A1A' ' state levels, we obtained rotationally resolved spectra for 16 of the 33 levels observed in our previous single vibronic level (SVL) emission study (Fan et al., J. Chem. Phys. 2005, 123, 014314), in addition to one new level. An anharmonic effective Hamiltonian model poorly reproduces the term energies even with the improved set of data because of the extensive interactions among levels in a given polyad (p) having combinations of nu1, nu2, nu3, which satisfy the relationship p = 2nu1 + nu2 + nu3. However, the precise A rotational constants determined from the SEP data were invaluable in clarifying the assignments for these strongly perturbed levels, and the data are well reproduced using a multiresonance effective Hamiltonian model. The derived vibrational parameters are in good agreement with high level ab initio calculations. The experimental frequencies were combined with those of CDF to derive a harmonic force field and average (rz,r(z)e) structures for the ground state.

Electronic spectroscopy of an isolated halocarbocation: the iodomethyl cation CH2I+ and its deuterated isotopomers.

Building upon our recent observation of the gas-phase electronic spectrum of the iodomethyl cation (CH2I+), we report an extensive study of the electronic spectroscopy of CH2I+ and its deuterated isotopomers CHDI+ and CD2I+ using a combination of fluorescence excitation and single vibronic level (SVL) emission spectroscopies. The spectra were measured in the gas phase under jet-cooled conditions using a pulsed discharge source. Fluorescence excitation spectra reveal a dominant progression in nu3 (C-I stretch), the frequency of which is markedly smaller in the upper state. Rotational analysis shows that, while the A constant is similar in the two states, the excited state has significantly smaller B and C constants. These results indicate a lengthening of the C-I bond upon electronic excitation, consistent with calculations which show that this transition is analogous to the well-known pi-pi* transition in the isoelectronic substituted formaldehydes. SVL emission spectra show progressions involving four of the six vibrational modes; only the C-H(D) stretching modes remain unobserved. The vibrational parameters determined from a Dunham expansion fit of the ground state vibrational term energies are in excellent agreement with the predictions of density functional theory (DFT) calculations. A normal-mode analysis was completed to derive a harmonic force field for the ground state, where resonance delocalization of the positive charge leads to partial double bond character, H2C+-I <--> H2C=I+, giving rise to a C-I stretching frequency significantly larger than that of the iodomethyl radical.

Observation of the predissociated, quasilinear B(1A') state of CHF by optical-optical double resonance.

We report the first observation of the predissociative B state of a halocarbene molecule. Rovibronic energy levels were measured in the B(1A') state of CHF by fluorescence dip detected optical-optical double resonance spectroscopy via the A state. The origin was found to lie 30 817.4 cm-1 above the zero point level of the X state. Rotational transitions within six purely bending states, and states involving one or two quanta of CF-stretch were observed, including the vibrational angular momentum components. Interpretation of the spectrum, with support of ab initio calculations, shows that CHF is quasilinear in the B state with a small (-200 cm-1) barrier to linearity which lies below the zero-point level. The rotational constant, B=1.04 to 1.09 cm-1, depending on vibrational state, again in good agreement with theory. All observed B state levels were predissociative, as evidenced by Lorentzian line broadening. Linewidths varied with initial state from 0.7-10.8 cm-1, corresponding to excited state lifetimes of 0.5-8 ps.

Probing spin-orbit mixing and the singlet-triplet gap in dichloromethylene via Ka-sorted emission spectra.

The magnitude of the singlet-triplet gap in dichloromethylene (CCl(2)) has been a point of controversy in the recent literature. In this study, we report single vibronic level emission spectra of the A(1)B(1)-->X[combining tilde](1)A(1) system of the carbene C(35)Cl(2), which probes the vibrational structure of the X[combining tilde](1)A(1) state up to approximately 10,000 cm(-1) above the vibrationless level. By the careful selection of bands where complete isotope and K(a)' selectivity in excitation was possible, we measured K(a)'-sorted emission spectra in order to test the previously established hypothesis [M.-L. Liu, C.-L. Lee, A. Bezant, G. Tarczay, R. J. Clark, T. A. Miller and B.-C. Chang, Phys. Chem. Chem. Phys., 2003, 5, 1352] that unassigned lines lying above approximately 5,000 cm(-1) belong to levels of the ã(3)B(1) state. The K(a)'-sorting method discriminates between singlet and triplet levels via the (A''-B[combining macron]'') rotational constant, which is significantly larger for pure triplet levels due to the larger equilibrium bond angle. In the region between 3,500 and 9,000 cm(-1) above the vibrationless level of the X[combining tilde](1)A(1) state, we find only a very modest increase in (A''-B[combining macron]''), and approximately 86% of the lines observed between 5,000 and 9,000 cm(-1) can be assigned to X[combining tilde](1)A(1) levels within 3 standard deviations of our Dunham expansion fit, which included more than 140 levels in total. A nearly complete set of Dunham parameters was determined for the C(35)Cl(2) isotopomer, and the X[combining tilde](1)A(1) state term energies up to 4,000 cm(-1) are in excellent agreement with recent variational calculations of Tarczay, et al. [G. Tarczay, T. A. Miller, G, Czakó and A. G. Császár, Phys. Chem. Chem. Phys., 2005, 7, 2881]. Finally, the implication of our results for the singlet-triplet gap in dichloromethylene is discussed.