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1.
Artigo em Inglês | MEDLINE | ID: mdl-38608239

RESUMO

Objectives: Although invasive cervical cancer (ICC) rates have declined since the advent of screening, the annual age-adjusted ICC rate in the United States remains 7.5 per 100,000 women. Failure of recommended screening and management often precedes ICC diagnoses. The study aimed to evaluate characteristics of women with incident ICC, including potential barriers to accessing preventive care. Materials and Methods: We abstracted medical records for patients with ICC identified during 2008-2020 in five U.S. population-based surveillance sites covering 1.5 million women. We identified evidence of adverse social and medical conditions, including uninsured/underinsured, language barrier, substance use disorder, incarceration, serious mental illness, severe obesity, or pregnancy at diagnosis. We calculated descriptive frequencies and compared potential barriers by race/ethnicity, and among women with and without symptoms at diagnosis using chi-square tests. Results: Among 1,606 women with ICC (median age: 49 years; non-White: 47.4%; stage I: 54.7%), the majority (68.8%) presented with symptoms. Forty-six percent of women had at least one identified potential barrier; 15% had multiple barriers. The most common potential barriers among all women were being underinsured/uninsured (17.3%), and language (17.1%). Presence of any potential barrier was more frequent among non-White women and women with than without symptoms (p < 0.05). Conclusions: In this population-based descriptive study of women with ICC, we identified adverse circumstances that might have prevented women from seeking screening and treatment to prevent cancer. Interventions to increase appropriate cervical cancer screening and management are critical for reducing cervical cancer rates.

2.
Int J Cancer ; 152(2): 137-150, 2023 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-35904861

RESUMO

Declines in cervical intraepithelial neoplasia grades 2 to 3 and adenocarcinoma in situ (CIN2+) observed among young women suggest impact from human papillomavirus (HPV) vaccination. To further evaluate vaccine impact including cross-protection and type replacement, we described high-risk (HR)-HPV type-specific cervical precancer incidence rates among women aged 20 to 39 years, 2008 to 2016. We analyzed cross-sectional population-based data on 18 344 cases of CIN2+ from a 5-site surveillance system. Diagnostic specimens were tested for individual HPV types, including 14 HR-HPV types (HPV16/18/31/33/35/39/45/51/52/56/58/59/66/68). We estimated age-specific annual HR-HPV type-specific CIN2+ incidence per 100 000 screened women for individual types, vaccine HR-HPV types (HPV16/18) and nonvaccine HR-HPV types (non-HPV16/18). We evaluated trends using average annual percent changes (AAPC) and 95% confidence intervals (CI), and estimated total declines by comparing 2015-2016 to 2008-2009 using incidence rate ratios. Among 20-24-year-olds, HPV16/18-CIN2+ declined from 2008 through 2016 (AAPC: -21.3%, 95% CI: -28.1%, -13.8%), whereas no trend was observed for non-HPV16/18-CIN2+ (AAPC: -1.8%, 95% CI: -8.1%, 4.9%). After 2010, CIN2+ among 20-24-year-olds was more often caused by nonvaccine vs vaccine HR-HPV types. No significant declining trends were observed in older age groups. In 2015-2016 compared with 2008-2009, HPV16-CIN2+ declined 78%, HPV18-CIN2+ 72% and HPV31-CIN2+ 51% among 20-24-year-olds; no increases were observed in type-specific CIN2+ incidence. Among 25-29-year-olds, HPV16-CIN2+ declined 18%; CIN2+ attributed to seven nonvaccine types increased significantly. No significant declines were observed in older groups. Significant declines in HPV16/18-CIN2+ in 20-24-year-olds and HPV16-CIN2+ in 25-29-year-olds corroborate impact of HPV vaccination. A declining trend in HPV31-CIN2+ is consistent with cross-protection from vaccination.


Assuntos
Vacinas contra Papillomavirus , Displasia do Colo do Útero , Neoplasias do Colo do Útero , Humanos , Feminino , Estados Unidos/epidemiologia , Idoso , Neoplasias do Colo do Útero/patologia , Estudos Transversais , Vacinas contra Papillomavirus/uso terapêutico , Papillomavirus Humano 16 , Papillomavirus Humano 31
3.
Sci Total Environ ; 821: 153355, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35093360

RESUMO

Food, energy, and water (FEW) are basic needs for well-being and quality of life. Assessing FEW security allows residents, communities, and policy makers to make informed decisions about how to sustain and improve well-being. We have developed a FEW security assessment framework that examines four components of security: availability, access, quality, and preference. With the help of local community members, we interviewed 114 households in three rural Alaska communities to assess FEW security, drivers and outcomes of FEW security, and potential interactions among FEW components and with renewable energy (RE) developments. While FEW security was high overall, preference and quality, especially for food, was lower. Food harvested from the local environment (i.e. subsistence) was necessary to include in security assessments given that 24% of participants reported insecurity when asked about contemporary sources (i.e. purchased) versus 5% reporting insecurity for subsistence food sources (i.e., harvested). The major influences on FEW security tended to originate from outside the community, including factors such as transportation, income, fuel prices, and weather. One internal factor, health, was both a driver and an outcome of FEW security. Satisfaction with RE varied (42%-68%) with dissatisfaction due to unreliability, uncertainty of the economic benefit, desire for other types of RE, or wanting more RE (n = 6). Communication about RE projects was key to managing expectations, promoting knowledge, and identifying benefits for residents. Participants did not identify linkages between RE and FEW security. Our assessment tool can be used by communities and policy makers to contextualize FEW security into more insightful and specific components, allowing for identification of attainable actions to improve FEW security and thus individual and community well-being.


Assuntos
Qualidade de Vida , Água , Alaska , Abastecimento de Alimentos , Humanos , População Rural , Abastecimento de Água
4.
J Homosex ; 69(12): 2104-2125, 2022 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-34612162

RESUMO

Research shows the critical value of teacher affirmation of LGBTQIA+ identities in improving social and academic outcomes for youth, and in rural areas this need is significant as students often experience discrimination with limited community resources. When provided, professional development is often concerned with safety and bullying with less focus on disrupting heteronormative and transphobic belief systems. Educators experience difficulty discussing these topics, however drawing upon a theory of a pedagogy of discomfort can help facilitators to foster critical thinking and engage learners in emotional labor leading to positive transformation. This article uses survey data to examine the impacts of pedagogical approaches of facilitators that invite and navigate discomfort in a workshop for educators on supporting LGBTQIA+ students in a rural district. Findings show that participants engage in challenging discussions, leading to deeper understandings, compassion, and the potential for positive action in school settings.


Assuntos
Bullying , Minorias Sexuais e de Gênero , Adolescente , Humanos , Instituições Acadêmicas , Estudantes/psicologia
5.
Vaccine ; 38(1): 39-45, 2020 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-31611099

RESUMO

We evaluated racial/ethnic differences in prevalence of oncogenic HPV types targeted by the quadrivalent HPV vaccine (16/18) and nonavalent HPV vaccine (31/33/45/52/58) in women diagnosed with CIN2/3/AIS after quadrivalent HPV vaccine introduction (2008-2015). Typing data from 1810 cervical tissue specimen from HPV-IMPACT (Alameda County, California, US), a population-based CIN2/3/AIS surveillance effort, were analyzed. Using log-binomial regression, we calculated adjusted prevalence ratios (aPR) and 95% confidence intervals (CI) comparing type prevalence by race/ethnicity, adjusted for health insurance, age, CIN2/3/AIS grade, and time period, overall and in the "early vaccine era" (2008-2011) and "later vaccine era" (2012-2015). Overall, oncogenic HPV16/18 prevalence was significantly lower among black (43%) and Hispanic (43%) women compared with white (52%) women (aPR (95% CI): 0.80 (0.70, 0.93) and 0.80 (0.70, 0.91), respectively). In 2008-2011, proportion of HPV16/18 detected was significantly lower in black (47%), Hispanic (46%), and Asian (42%) women compared to white (58%) women (aPR (95% CI): 0.80 (0.67, 0.96), 0.75 (0.63, 0.90), and 0.73 (0.58, 0.90), respectively). There were no significant differences in 2012-2015. Between the two eras, HPV16/18 prevalence declined in white (-11%), black (-9%), and Hispanic (-6%) women, and increased in Asian women (12%). Decreasing HPV 16/18 prevalence in CIN2/3/AIS lesions in white, black, and Hispanic women may suggest benefit from quadrivalent vaccination. In our unadjusted analysis of HPV31/33/45/52/58, prevalence did not differ significantly by race/ethnicity, but was significantly higher among Hispanic women (32%) compared to white women (27%) after adjustment (aPR (95%CI): 1.22 (1.02, 1.47). Prevalence was also non-significantly higher among black (32%) and Asian (33%) women. This analysis suggests that the nonavalent vaccine's potential for impact against cervical precancers will not be lower in women of color compared to white women. These data underscore the importance of equitable vaccination in facilitating continued declines of vaccine-preventable HPV types among all women.


Assuntos
Etnicidade , Vacinas contra Papillomavirus/administração & dosagem , Grupos Raciais/etnologia , Fatores Socioeconômicos , Displasia do Colo do Útero/etnologia , Neoplasias do Colo do Útero/etnologia , Adolescente , Adulto , California/etnologia , Feminino , Humanos , Gradação de Tumores/métodos , Prevalência , Estados Unidos/etnologia , Neoplasias do Colo do Útero/diagnóstico , Neoplasias do Colo do Útero/prevenção & controle , Adulto Jovem , Displasia do Colo do Útero/diagnóstico , Displasia do Colo do Útero/prevenção & controle
6.
Environ Eng Sci ; 36(7): 843-849, 2019 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-31346306

RESUMO

In recent years, there has been increased recognition of the importance of a nexus approach to optimize food, energy, and water (FEW) security at regional and global scales. Remote communities in the Arctic and Subarctic regions in Alaska provide unique examples of closed and isolated systems, wherein the FEW nexus not only needs to be examined to lend resilience to these vulnerable communities but that could also serve as small-scale test beds for a wider and systematic understanding of the FEW nexus. In this short communication, looking at the FEW nexus in Cordova, Alaska, through an energy lens, we introduce an approach (referred to as the "MicroFEWs approach") that may assist remote communities in Alaska in making informed decisions regarding the use of renewable energy to increase FEW security. Our example uses the MicroFEWs approach to assess the impacts of increased renewable energy generation on FEW security in the community, more specifically to food security through potential changes to the community's fish processing industry. This approach can serve as a basis for investigating the FEW nexus in varying contexts and locales.

7.
MMWR Morb Mortal Wkly Rep ; 68(15): 337-343, 2019 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-30998672

RESUMO

Human papillomavirus (HPV) causes approximately 30,000 cancers in the United States annually (1). HPV vaccination was introduced in 2006 to prevent HPV-associated cancers and diseases (1). Cervical cancer is the most common HPV-associated cancer in women (1). Whereas HPV-associated cancers typically take decades to develop, screen-detected high-grade cervical lesions (cervical intraepithelial neoplasia grades 2 [CIN2], 3 [CIN3], and adenocarcinoma in situ, collectively CIN2+) develop within a few years after infection and have been used to monitor HPV vaccine impact (1-3). CDC analyzed data from the Human Papillomavirus Vaccine Impact Monitoring Project (HPV-IMPACT), a population-based CIN2+ surveillance system, to describe rates of CIN2+ among women aged ≥18 years during 2008-2016. Age-specific rates were applied to U.S. population data to estimate the total number of CIN2+ cases diagnosed in the United States in 2008* and in 2016. From 2008 to 2016, the rate of CIN2+ per 100,000 women declined significantly in women aged 18-19 years and 20-24 years and increased significantly in women aged 40-64 years. In the United States in 2008, an estimated 216,000 (95% confidence interval [CI] = 194,000-241,000) CIN2+ cases were diagnosed, 55% of which were in women aged 18-29 years; in 2016, an estimated 196,000 (95% CI = 176,000-221,000) CIN2+ cases were diagnosed, 36% of which were in women aged 18-29 years. During 2008 and 2016, an estimated 76% of CIN2+ cases were attributable to HPV types targeted by the vaccine currently used in the United States. These estimates of CIN2+ cases likely reflect changes in CIN2+ detection resulting from updated cervical cancer screening and management recommendations, as well as primary prevention through HPV vaccination. Increasing coverage of HPV vaccination in females at the routine age of 11 or 12 years and catch-up vaccination through age 26 years will contribute to further reduction in cervical precancers.


Assuntos
Neoplasias do Colo do Útero/diagnóstico , Neoplasias do Colo do Útero/epidemiologia , Adolescente , Adulto , Idoso , Feminino , Humanos , Pessoa de Meia-Idade , Gradação de Tumores , Vacinas contra Papillomavirus/administração & dosagem , Estados Unidos/epidemiologia , Adulto Jovem
8.
Papillomavirus Res ; 7: 141-149, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30980966

RESUMO

INTRODUCTION: Evidence of human papillomavirus (HPV) vaccine impact on anogenital warts (AGWs) by race or urbanicity in the US is lacking. We evaluated HPV vaccine impact in Tennessee by assessing AGW trends among Tennessee Medicaid (TennCare) enrollees aged 15-39 years from 2006-2014. METHODS: Persons with incident AGWs were identified using diagnosis/pharmacy codes from TennCare billing claims. We calculated sex-specific annual AGW incidence by age group, race, and urbanicity; estimated annual percent changes (APCs) using log-linear models; and performed pairwise comparisons by race and urbanicity. RESULTS: AGW incidence decreased among females aged 15-19 (APC = -10.6; P < 0.01) and 20-24 years (APC = -3.9; P = 0.02). Overall trends were similar between Whites and Blacks, and between those living in metropolitan statistical areas (MSAs) and non-MSAs. Rates among males aged 15-19 years began decreasing after 2010. Among enrollees aged 25-39 years, rates increased or were stable. CONCLUSIONS: Following introduction of the HPV vaccine in 2006, AGWs decreased among age groups most likely to be vaccinated. The change in trend among young males after 2010 suggests early herd effects. Our findings indicate vaccine effects and support the importance of improving adherence to current vaccination recommendations for preventing AGWs and other HPV-related diseases.


Assuntos
Doenças do Ânus/epidemiologia , Doenças do Ânus/prevenção & controle , Condiloma Acuminado/epidemiologia , Condiloma Acuminado/prevenção & controle , Vacinas contra Papillomavirus/imunologia , Adolescente , Adulto , Fatores Etários , Feminino , Humanos , Incidência , Masculino , Medicaid , Vacinas contra Papillomavirus/administração & dosagem , Fatores Raciais , Tennessee/epidemiologia , Estados Unidos , Adulto Jovem
9.
Clin Infect Dis ; 68(8): 1282-1291, 2019 04 08.
Artigo em Inglês | MEDLINE | ID: mdl-30137283

RESUMO

BACKGROUND: We describe changes in rates of cervical intraepithelial neoplasia grades 2, 3 and adenocarcinoma in situ (CIN2+) during a period of human papillomavirus (HPV) vaccine uptake and changing cervical cancer screening recommendations. METHODS: We conducted population-based laboratory surveillance for CIN2+ in catchment areas in 5 states, 2008-2015. We calculated age-specific CIN2+ rates per 100000 women by age groups. We estimated incidence rate ratios (IRR) of CIN2+ for 2-year periods among all women and among screened women to evaluate changes over time. RESULTS: A total of 16572 CIN2+ cases were reported. Among women aged 18-20 and 21-24 years, CIN2+ rates declined in all sites, whereas in women aged 25-29, 30-34, and 35-39 years, trends differed across sites. The percent of women screened annually declined in all sites and age groups. Compared to 2008-2009, rates among screened women were significantly lower for all 3 periods in women aged 18-20 years (2010-2011: IRR 0.82, 95% confidence interval [CI] 0.67-0.99; 2012-2013: IRR 0.63, 95% CI 0.47-0.85; 2014-2015: IRR 0.44, 95% CI 0.28-0.68) and lower for the latter 2 time periods in women aged 21-24 years (2012-2013: IRR 0.86, 95% CI 0.79-0.94; 2014-2015: IRR 0.61, 95% CI 0.55-0.67). CONCLUSIONS: From 2008-2015, both CIN2+ rates and cervical cancer screening declined in women aged 18-24 years. The significant decreases in CIN2+ rates among screened women aged 18-24 years are consistent with a population-level impact of HPV vaccination.


Assuntos
Adenocarcinoma in Situ/epidemiologia , Detecção Precoce de Câncer/tendências , Vacinas contra Papillomavirus/administração & dosagem , Displasia do Colo do Útero/epidemiologia , Neoplasias do Colo do Útero/epidemiologia , Adolescente , Adulto , Feminino , Humanos , Estados Unidos/epidemiologia , Adulto Jovem
10.
Emerg Infect Dis ; 21(9): 1557-61, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26291379

RESUMO

In 2007, five Emerging Infections Program (EIP) sites were funded to determine the feasibility of establishing a population-based surveillance system for monitoring the effect of human papillomavirus (HPV) vaccine on pre-invasive cervical lesions. The project involved active population-based surveillance of cervical intraepithelial neoplasia grades 2 and 3 and adenocarcinoma in situ as well as associated HPV types in women >18 years of age residing in defined catchment areas; collecting relevant clinical information and detailed HPV vaccination histories for women 18-39 years of age; and estimating the annual rate of cervical cancer screening among the catchment area population. The first few years of the project provided key information, including data on HPV type distribution, before expected effect of vaccine introduction. The project's success exemplifies the flexibility of EIP's network to expand core activities to include emerging surveillance needs beyond acute infectious diseases. Project results contribute key information regarding the impact of HPV vaccination in the United States.


Assuntos
Doenças Transmissíveis Emergentes/epidemiologia , Infecções por Papillomavirus/epidemiologia , Adolescente , Adulto , Doenças Transmissíveis Emergentes/prevenção & controle , Feminino , Humanos , Pessoa de Meia-Idade , Avaliação de Resultados em Cuidados de Saúde , Infecções por Papillomavirus/prevenção & controle , Vacinas contra Papillomavirus/administração & dosagem , Vigilância em Saúde Pública , Estados Unidos/epidemiologia , Neoplasias do Colo do Útero/epidemiologia , Neoplasias do Colo do Útero/prevenção & controle , Vacinação , Saúde da Mulher , Adulto Jovem , Displasia do Colo do Útero/epidemiologia , Displasia do Colo do Útero/prevenção & controle
11.
Vaccine ; 33(13): 1608-13, 2015 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-25681664

RESUMO

BACKGROUND: Prevention of pre-invasive cervical lesions is an important benefit of HPV vaccines, but demonstrating impact on these lesions is impeded by changes in cervical cancer screening. Monitoring vaccine-types associated with lesions can help distinguish vaccine impact from screening effects. We examined trends in prevalence of HPV 16/18 types detected in cervical intraepithelial neoplasia 2, 3, and adenocarcinoma in situ (CIN2+) among women diagnosed with CIN2+ from 2008 to 2012 by vaccination status. We estimated vaccine effectiveness against HPV 16/18-attributable CIN2+ among women who received ≥1 dose by increasing time intervals between date of first vaccination and the screening test that led to detection of CIN2+ lesion. METHODS: Data are from a population-based sentinel surveillance system to monitor HPV vaccine impact on type-specific CIN2+ among adult female residents of five catchment areas in California, Connecticut, New York, Oregon, and Tennessee. Vaccination and cervical cancer screening information was retrieved. Archived diagnostic specimens were obtained from reporting laboratories for HPV DNA typing. RESULTS: From 2008 to 2012, prevalence of HPV 16/18 in CIN2+ lesions statistically significantly decreased from 53.6% to 28.4% among women who received at least one dose (Ptrend<.001) but not among unvaccinated women (57.1% vs 52.5%; Ptrend=.08) or women with unknown vaccination status (55.0% vs 50.5%; Ptrend=.71). Estimated vaccine effectiveness for prevention of HPV 16/18-attributable CIN2+ was 21% (95% CI: 1-37), 49% (95% CI: 28-64), and 72% (95% CI: 45-86) in women who initiated vaccination 25-36 months, 37-48 months, and >48 months prior to the screening test that led to CIN2+ diagnosis. CONCLUSIONS: Population-based data from the United States indicate significant reductions in CIN2+ lesions attributable to types targeted by the vaccines and increasing HPV vaccine effectiveness with increasing interval between first vaccination and earliest detection of cervical disease.


Assuntos
Adenocarcinoma in Situ/prevenção & controle , Papillomavirus Humano 16/isolamento & purificação , Papillomavirus Humano 18/isolamento & purificação , Vacinas contra Papillomavirus/uso terapêutico , Doenças do Colo do Útero/prevenção & controle , Displasia do Colo do Útero/prevenção & controle , Adenocarcinoma in Situ/diagnóstico , Adenocarcinoma in Situ/virologia , Adulto , California , Connecticut , Detecção Precoce de Câncer , Feminino , Humanos , New York , Oregon , Vacinas contra Papillomavirus/administração & dosagem , Prevalência , Vigilância de Evento Sentinela , Tennessee , Fatores de Tempo , Estados Unidos , Vacinação , Adulto Jovem , Displasia do Colo do Útero/diagnóstico , Displasia do Colo do Útero/virologia
12.
Scand J Infect Dis ; 40(11-12): 888-93, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18728934

RESUMO

The association between tuberculosis (TB) and diabetes is re-emerging with the epidemic of type 2 diabetes (T2DM). We analyzed retrospective data from 2878 TB patients across the Texas/Mexico border. Overall, 161/2878 (5.6%) patients had MDR TB (resistance to rifampin and isoniazid): Texas 49/1442 (3.4%) and Mexico 112/1436 (7.8%). In Texas, MDR TB was significantly associated with T2DM (OR 2.1, 95% CI 1.1-4.2) when adjusted for age, gender, drug and alcohol abuse, HIV infection and history of previous episode of TB; and in Mexico (OR 1.80, 95% CI 1.1-2.9) when adjusted for age and gender. Patients with T2DM in both countries were more likely to be compliant with DOTS therapy (Texas: OR 2.4, 95% CI 1.1-5.4) than patients without T2DM. In Texas, all but 3 of the T2DM patients with MDR TB were resistant at their first culture at the time of diagnosis. It is possible that impaired immunity in T2DM increases susceptibility to infection with resistant strains.


Assuntos
Diabetes Mellitus Tipo 2/complicações , Tuberculose Resistente a Múltiplos Medicamentos/complicações , Adulto , Idoso , Feminino , Humanos , Masculino , Americanos Mexicanos , México , Pessoa de Meia-Idade , Razão de Chances , Risco
13.
J Chem Phys ; 125(5): 054303, 2006 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-16942209

RESUMO

First high-resolution infrared spectra are presented for jet-cooled CH2 35Cl and CH2 37Cl radicals in the symmetric (nu1) CH2 stretching mode. A detailed spectral assignment yields refined lower and upper state rotational constants, as well as fine structure spin-rotation parameters from least-squares fits to the sub-Doppler line shapes for individual transitions. The rotational constants are consistent with a nearly planar structure, but do not exclude substantial large amplitude bending motion over a small barrier to planarity accessible with zero-point excitation. High level coupled cluster (singles/doubles/triples) calculations, extrapolated to the complete basis set limit, predict a slightly nonplanar equilibrium structure (theta approximately 11 degrees), with a vibrationally adiabatic treatment of the bend coordinate yielding a v = 1<--0 anharmonic frequency (393 cm(-1)) in excellent agreement with matrix studies (nu(bend) approximately 400 cm(-1)). The antisymmetric CH2 stretch vibration is not observed despite high sensitivity detection (signal to noise ratio >20:1) in the symmetric stretch band. This is consistent with density functional theory intensity calculations indicating a >35-fold smaller antisymmetric stretch transition moment for CH2Cl, and yet contrasts dramatically with high-resolution infrared studies of CH2F radical, for which both symmetric and antisymmetric CH2 stretches are observed in a nearly 2:1 intensity ratio. A simple physical model is presented based on a competition between bond-dipole and "charge-sloshing" contributions to the transition moment, which nicely explains the trends in CH2X symmetric versus asymmetric stretch intensities as a function of electron withdrawing group (X = D,Br,Cl,F).

14.
J Chem Phys ; 125(5): 054304, 2006 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-16942210

RESUMO

The combination of shot noise-limited direct absorption spectroscopy with long-path-length slit supersonic discharges has been used to obtain first high-resolution infrared spectra for jet-cooled CH2F radicals in the symmetric (nu1) and antisymmetric (nu5) CH2 stretching modes. Spectral assignment has yielded refined lower- and upper-state rotational constants and fine-structure parameters from least-squares fits to the sub-Doppler line shapes for individual transitions. The rotational constants provide indications of large amplitude vibrational averaging over a low-barrier double minimum inversion-bending potential. This behavior is confirmed by high-level coupled cluster singles/doubles/triples calculations extrapolated to the complete basis set limit and adiabatically corrected for zero point energy. The calculations predict a nonplanar equilibrium structure (theta approximately 29 degrees, where theta is defined to be 180 degrees minus the angle between the C-F bond and the CH2 plane) with a 132 cm(-1) barrier to planarity and a vibrational bend frequency (nu(bend) approximately 276 cm(-1)), in good agreement with previous microwave estimates (nu(bend) = 300 (30) cm(-1)) by Hirota and co-workers [Y. Endo et al., J. Chem. Phys. 79, 1605 (1983)]. The nearly 2:1 ratio of absorption intensities for the symmetric versus antisymmetric bands is in good agreement with density functional theory calculations, but in sixfold contrast with simple local mode CH2 bond dipole predictions of 1:3. This discrepancy arises from a surprisingly strong dependence of the symmetric stretch intensity on the inversion bend angle and provides further experimental support for a nonplanar equilibrium structure.

15.
J Chem Phys ; 122(12): 124310, 2005 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-15836381

RESUMO

State-to-state scattering dynamics of F+C2H6-->HF(v,J)+C2H5 have been investigated at Ecom=3.2(6) kcalmol under single-collision conditions, via detection of nascent rovibrationally resolved HF(v,J) product states with high-resolution infrared laser absorption methods. State-resolved Doppler absorption profiles are recorded for multiple HF(v,J) transitions originating in the v=0,1,2,3 manifold, analyzed to yield absolute column-integrated densities via known HF transition moments, and converted into nascent probabilities via density-to-flux analysis. The spectral resolution of the probe laser also permits Doppler study of translational energy release into quantum-state-resolved HF fragments, which reveals a remarkable linear correlation between (i) HF(v,J) translational recoil and (ii) the remaining energy available, Eavail=Etot-E(HF(v,J)). The dynamics are interpreted in the context of a simple impulsive model based on conservation of linearangular momentum that yields predictions in good agreement with experiment. Deviations from the model indicate only minor excitation of ethyl vibrations, in contrast with a picture of extensive intramolecular vibrational energy flow but consistent with Franck-Condon excitation of the methylene CH2 bending mode. The results suggest a relatively simple dynamical picture for exothermic atom+polyatomic scattering, i.e., that of early barrier dynamics in atom+diatom systems but modified by impulsive recoil coupling at the transition state between translationalrotational degrees of freedom.

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