Prevalence, Predictors, and Outcomes of Type 2 NSTEMI in Hospitalized Patients With COVID-19.

BACKGROUND: Data on the incidence of type 2 non-ST-segment-elevation myocardial infarction (T2MI) in hospitalized patients with COVID-19 has been limited to single-center studies. Given that certain characteristics, such as obesity and type 2 diabetes, have been associated with higher mortality in COVID-19 infections, we aimed to define the incidence of T2MI in a national cohort and identify pre-hospital patient characteristics associated with T2MI in hospitalized patients with COVID-19. METHODS AND RESULTS: Using the national American Heart Association COVID-19 Cardiovascular Disease Quality Improvement Registry, we performed a retrospective 4:1 matched (age, sex, race, and body mass index) analysis of controls versus cases with T2MI. We performed (1) conditional multivariable logistic regression to identify predictive pre-hospital patient characteristics of T2MI for patients hospitalized with COVID-19 and (2) stratified proportional hazards regression to investigate the association of T2MI with morbidity and mortality. From January 2020 through May 2021, there were 709 (2.2%) out of 32 015 patients with T2MI. Five hundred seventy-nine cases with T2MI were matched to 2171 controls (mean age 70; 43% female). Known coronary artery disease, heart failure, chronic kidney disease, hypertension, payor source, and presenting heart rate were associated with higher odds of T2MI. Anti-hyperglycemic medication and anti-coagulation use before admission were associated with lower odds of T2MI. Those with T2MI had higher morbidity and mortality (hazard ratio, 1.40 [95% CI, 1.13-1.74]; P=0.002). CONCLUSIONS: In hospitalized patients with COVID-19, those with a T2MI compared with those without had higher morbidity and mortality. Outpatient anti-hyperglycemic and anti-coagulation use were the only pre-admission factors associated with reduced odds of T2MI.

Late-onset rupture of an intracranial dermoid cyst: a case report.

BACKGROUND: Dermoid cysts are developmental abnormalities occurring between the third and fifth week of embryogenesis. These lesions can initially develop as intracranial or extracranial and persist throughout the patient's lifetime. While generally benign, their symptoms can be due to mass effect or local irritation secondary to rupture and release of contents, typically presenting as headaches and seizures. Intracranial dermoid cysts are rare and comprise less than 1% of all intracranial lesions, with rupture occurring approximately 0.18% of the time. CASE PRESENTATION: Our case describes a 42-year-old Hispanic female with a late-onset rupture of an intracranial dermoid cyst with associated new onset seizures. She underwent uncomplicated neurosurgical resection with mesh placement and was scheduled to follow-up as an outpatient. CONCLUSION: To avoid rupture and associated sequelae in future patients, we recommend considering a more invasive approach as the initial strategy if internal cysts are relatively accessible.

CT-guided microwave ablation of the nonsurgical aspergilloma.

Background: Aspergillosis is a fungal infection that can lead to development of an aspergilloma, especially in patients with a history of cavitary lung disease. It is generally managed with antifungal therapy followed by surgical intervention. There are, however, limited options for the nonsurgical patient. Microwave ablation is already an effective, minimally invasive treatment being used in some lung malignancies and may be an alternative and definitive treatment in the inoperable patient. Methods: Two patients were considered for microwave ablation following their diagnoses of aspergillosis with hemoptysis. We sought to evaluate the efficacy of CT-guided microwave ablation of an aspergilloma in these patients who were not good candidates for surgical intervention. Results: Two male patients presented with hemoptysis and were found to have an aspergilloma. Case 1 was initially treated with antifungals and did not improve. He proceeded with VATS, and the procedure was aborted intraoperatively secondary to a frozen chest cavity. The patient subsequently elected to undergo CT-guided microwave ablation. He did not experience any immediate complications but was hospitalized for hemoptysis several weeks later. He developed alveolar hemorrhage and ultimately succumbed to PEA arrest.Case 2 was without hemoptysis at follow up and chose to pursue microwave ablation for definitive treatment. Case 2 developed post ablation pneumothorax requiring chest tube placement. Follow-up CT chest imaging was consistent with resolution of the aspergilloma. Conclusion: Microwave ablation is a safe and effective therapeutic approach in the treatment of lung malignancy with no severe or death related complications. There are almost no absolute contraindications. Microwave ablation may be utilized as a therapeutic option in the treatment of an aspergilloma in the non-surgical patient. This novel application may challenge the current gold standard of surgical intervention.

Collagen-Specific HSP47+ Myofibroblasts and CD163+ Macrophages Identify Profibrotic Phenotypes in Deceased Hearts With SARS-CoV-2 Infections.

Background Cardiac fibrosis complicates SARS-CoV-2 infections and has been linked to arrhythmic complications in survivors. Accordingly, we sought evidence of increased HSP47 (heat shock protein 47), a stress-inducible chaperone protein that regulates biosynthesis and secretion of procollagen in heart tissue, with the goal of elucidating molecular mechanisms underlying cardiac fibrosis in subjects with this viral infection. Methods and Results Using human autopsy tissue, immunofluorescence, and immunohistochemistry, we quantified Hsp47+ cells and collagen α 1(l) in hearts from people with SARS-CoV-2 infections. Because macrophages are also linked to inflammation, we measured CD163+ cells in the same tissues. We observed irregular groups of spindle-shaped HSP47+ and CD163+ cells as well as increased collagen α 1(I) deposition, each proximate to one another in "hot spots" of ≈40% of hearts after SARS-CoV-2 infection (HSP47+ P<0.05 versus nonfibrotics and P<0.001 versus controls). Because HSP47+ cells are consistent with myofibroblasts, subjects with hot spots are termed "profibrotic." The remaining 60% of subjects dying with COVID-19 without hot spots are referred to as "nonfibrotic." No control subject exhibited hot spots. Conclusions Colocalization of myofibroblasts, M2(CD163+) macrophages, and collagen α 1(l) may be the first evidence of a COVID-19-related "profibrotic phenotype" in human hearts in situ. The potential public health and diagnostic implications of these observations require follow-up to further define mechanisms of viral-mediated cardiac fibrosis.

Internal herniation of the right colon through the foramen of Winslow: A case report.

INTRODUCTION AND IMPORTANCE: Herniation through the Foramen of Winslow, also known as the epiploic foramen, is an extremely rare phenomenon with less than 200 cases reported in medical literature. Internal hernias account for less than 1% of all hernias and roughly 8% of all internal hernias occur through the foramen of Winslow. We present a case of a foramen of Winslow hernia that was not detected until direct visualization with laparoscopy. PRESENTATION OF CASE: A 52 year-old healthy female with a surgical history of a Caesarean section presented to the ER with severe epigastric pain radiating to her back. Physical exam was positive for abdominal tenderness and guarding. Vital signs were within normal limits. Murphy's sign and Rovsing's sign were negative. Initial imaging studies, including a CT scan of the abdomen, and laboratory findings were unremarkable. A hepatobiliary iminodiacetic acid (HIDA) scan was performed and demonstrated non-visualization of the gallbladder suggestive of acute vs. chronic cholecystitis. Following these results the patient elected to undergo exploratory laparoscopy with potential cholecystectomy. Intra-operatively, the colon was noted to be herniated through the foramen of Winslow. The procedure was converted to an open laparotomy. The hernia was manually reduced, and a right hemicolectomy was performed to prevent recurrence of the hernia. DISCUSSION: Reports list an enlarged foramen of Winslow, excessive viscera mobility (i.e., persistent ascending mesocolon or long small bowel mesentery), and an increase in intra-abdominal pressure as potential risk factors for this particular hernia. In our case, the patient was noted to have excessive mobility of the viscera with the presence of persistent ascending mesocolon and an abnormally long right mesentery. Physical exam is usually nonspecific and laboratory findings are typically unremarkable, posing a diagnostic challenge. Additionally, radiological findings indicating presence of an internal hernia were missed in the initial CT scan read by the radiologist. Internal hernias need to be managed surgically as there is a risk of strangulation with bowel ischemia. CONCLUSION: This rare radiographic phenomenon is difficult to diagnose radiographically and warrants further workup due to the potential risk of bowel strangulation despite negative clinical and laboratory findings.

A Triad of Pericarditis, Pericardial Effusion, and Pleural Effusion as the Predominant Presentation of Rheumatoid Arthritis - A Case Report.

We describe a case of a 67-year-old African American man who presented to the emergency department with a sharp, pleuritic chest pain and shortness of breath. After several admissions and extensive workup, he ultimately was diagnosed with a persistent pleural effusion, pericardial effusion, and secondary constrictive pericarditis due to rheumatoid arthritis. By highlighting immunological disorders such as rheumatoid arthritis in the differential diagnosis, in the setting of a refractory pericardial effusion and serositis, this case report addresses key aspects of the presentation both in the emergency and inpatient settings, reviews the criteria for a rheumatoid arthritis diagnosis, and emphasizes areas of importance in predominantly cardiopulmonary extra-articular manifestations of a typically musculoskeletal disease.

Noninvasive Neurally Adjusted Ventilatory Assist Versus High Flow Cannula Support After Congenital Heart Surgery.

BACKGROUND: Extubation failure rates for critical patients in pediatric intensive care units (ICUs) range from 5% to 29%. Noninvasive (NIV) ventilation has been shown to decrease extubation failure. We compared reintubation rates and outcomes of patients supported with NIV neurally adjusted ventilation assist (NAVA) versus historical controls supported with high-flow nasal cannula (HFNC). METHODS: Case-control study of infants less than three months of age who underwent cardiac surgery and received NIV support after extubation from January 2011 to May 2017. All patients supported with NIV NAVA after it became available in September 2013 were compared to matched patients extubated to HFNC from prior to September 2013. RESULTS: Forty-two patients identified for the NIV NAVA group were matched with 42 historical controls supported with HFNC. Groups had similar baseline characteristics based on rate of acute kidney injury, number of single ventricle patients, Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery (STAT) category, age, weight, bypass time, and duration of intubation. There was no significant difference in reintubation rates within 72 hours (14.3% in the HFNC group and 16.7% in the NIV NAVA group, P = 1.0). Median duration from extubation to coming off NIV support was longer in the NIV NAVA group (3.6 days vs 0.6 days, P < .001). Median time from extubation to ICU discharge was longer in the NIV NAVA group (10.5 vs 6.8 days, P = .02), as was total postoperative ICU length of stay (LOS; 17.6 vs 12.2, P = .01). CONCLUSIONS: Introduction of NIV NAVA for postextubation support did not reduce reintubation rates compared to HFNC. Further study is needed as adoption of NIV NAVA may prolong LOS.

Near-UV photolysis of substituted phenols. Part II. 4-, 3- and 2-methylphenol.

The photodissociation of jet-cooled 4-, 3- and 2-methylphenol molecules has been investigated using the experimental techniques of resonance enhanced multiphoton ionisation and H (Rydberg) atom photofragment translational spectroscopy. O-H bond fission is found to occur, via a repulsive (1)pisigma state, in a manner analogous to that occurring in phenol and 4-fluorophenol. Excitation to the (1)pipi manifold results in H-atom loss either directly (via a (1)pipi/(1)pisigma conical intersection) or indirectly, following internal conversion to the ground state and subsequent coupling to the (1)pisigma state via a second conical intersection at extended O-H bond lengths. The resulting methylphenoxyl radicals are created with specific vibrational excitation, reflecting the nuclear distortions required to access the (1)pisigma potential energy surface and the geometry changes induced by subsequent H atom loss. The position of the methyl group on the benzene ring is observed to influence the product vibrational energy disposal-not least through its influence on the mode(s) that are activated as a result of coupling to the repulsive (1)pisigma state. O-H bond strengths are reported for 4-, 3- and 2-methylphenol. These are in good agreement with values derived from recent combustion calorimetry studies and serve to highlight the relative destabilisation of the radical caused by methyl substitution at the 3-position.

Quantitative (upsilon, N, Ka) product state distributions near the triplet threshold for the reaction H2CO --> H + HCO measured by Rydberg tagging and laser-induced fluorescence.

In this paper, we report quantitative product state distributions for the photolysis of H2CO --> H + HCO in the triplet threshold region, specifically for several rotational states in the 2(2)4(3) and 2(3)4(1) H2CO vibrational states that lie in this region. We have combined the strengths of two complementary techniques, laser-induced fluorescence for fine resolution and H atom Rydberg tagging for the overall distribution, to quantify the upsilon, N, and Ka distributions of the HCO photofragment formed via the singlet and triplet dissociation mechanisms. Both techniques are in quantitative agreement where they overlap and provide calibration or benchmarks that permit extension of the results beyond that possible by each technique on its own. In general agreement with previous studies, broad N and Ka distributions are attributed to reaction on the S0 surface, while narrower distributions are associated with reaction on T1. The broad N and Ka distributions are modeled well by phase space theory. The narrower N and Ka distributions are in good agreement with previous quasi-classical trajectory calculations on the T1 surface. The two techniques are combined to provide quantitative vibrational populations for each initial H2CO vibrational state. For dissociation via the 2(3)4(1) state, the average product vibrational energy (15% of E(avail)) was found to be about half of the rotational energy (30% of E(avail)), independent of the initial H2CO rotational state, irrespective of the singlet or triplet mechanism. For dissociation via the 2(2)4(3) state, the rotational excitation remained about 30% of E(avail), but the vibrational excitation was reduced.

Near-ultraviolet photodissociation of thiophenol.

H(D) Rydberg atom photofragment translational spectroscopy has been used to investigate the dynamics of H(D) atom loss C6H5SH(C6H5SD) following excitation at many wavelengths lambda phot in the range of 225-290 nm. The C6H5S cofragments are formed in both their ground (X(2)B1) and first excited ((2)B2) electronic states, in a distribution of vibrational levels that spreads and shifts to higher internal energies as lambda(phot) is reduced. Excitation at lambda(phot) > 275 nm populates levels of the first (1)pi pi* state, which decay by tunnelling to the dissociative (1)pi sigma* state potential energy surface (PES). S-H torsional motion is identified as a coupling mode facilitating population transfer at the conical intersection (CI) between the diabatic (1)pi pi* and (1)pi sigma* PESs. At shorter lambda(phot), the (1)pi sigma* state is deduced to be populated either directly or by efficient vibronic coupling from higher (1)pipi* states. Flux evolving on the (1)pi sigma* PES samples a second CI, at longer R(S-H), between the diabatic (1)pi sigma* and ground ((1)pi pi) PESs, where the electronic branching between ground and excited state C6H5S fragments is determined. The C6H5S(X(2)B1) and C6H5S((2)B2) products are deduced to be formed in levels with, respectively, a' and a'' vibrational symmetry-behavior that reflects both Franck-Condon effects (both in the initial photoexcitation step and in the subsequent in-plane forces acting during dissociation) and the effects of the out-of-plane coupling mode(s), nu11 and nu16a, at the (1)pi sigma*/(1)pi pi CI. The vibrational state assignments enabled by the high-energy resolution of the present data allow new and improved estimations of the bond dissociation energies, D0(C6H5S-H) < or = 28,030 +/- 100 cm(-1) and D0(C6H5S-D) < or = 28,610 +/- 100 cm(-1), and of the energy separation between the X(2)B1 and (2)B2 states of the C6H5S radical, T(00) = 2800 +/- 40 cm(-1). Similarities, and differences, between the measured energy disposals accompanying UV photoinduced X-H (X = S, O) bond fission in thiophenol and phenol are discussed.

Exploring nuclear motion through conical intersections in the UV photodissociation of phenols and thiophenol.

High-resolution time-of-flight measurements of H atom products from photolysis of phenol, 4-methylphenol, 4-fluorophenol, and thiophenol, at many UV wavelengths (lambda(phot)), have allowed systematic study of the influence of ring substituents and the heteroatom on the fragmentation dynamics. All dissociate by X-H (X = O, S) bond fission after excitation at their respective S(1)((1)pipi*)-S(0) origins and at all shorter wavelengths. The achieved kinetic energy resolution reveals population of selected vibrational levels of the various phenoxyl and thiophenoxyl coproducts, providing uniquely detailed insights into the fragmentation dynamics. Dissociation in all cases is deduced to involve nuclear motion on the (1)pisigma* potential energy surface (PES). The route to accessing this PES, and the subsequent dynamics, is seen to be very sensitive to lambda(phot) and substitution of the heteroatom. In the case of the phenols, dissociation after excitation at long lambda(phot) is rationalized in terms of radiationless transfer from S(1) to S(0) levels carrying sufficient O-H stretch vibrational energy to allow coupling via the conical intersection between the S(0) and (1)pisigma* PESs at longer O-H bond lengths. In contrast, H + C(6)H(5)O(X(2)B(1)) products formed after excitation at short lambda(phot) exhibit anisotropic recoil-velocity distributions, consistent with prompt dissociation induced by coupling between the photoprepared (1)pipi* excited state and the (1)pisigma* PES. The fragmentation dynamics of thiophenol at all lambda(phot) matches the latter behavior more closely, reflecting the different relative dispositions of the (1)pipi* and (1)pisigma* PESs. Additional insights are provided by the observed branching into the ground (X(2)B(1)) and first excited ((2)B(2)) states of the resulting C(6)H(5)S radicals.

State-selective photodissociation dynamics of formaldehyde: near threshold studies of the H+HCO product channel.

The laser-induced photodissociation of formaldehyde in the wavelength range 309

Near-UV photolysis of substituted phenols, I: 4-fluoro-, 4-chloro- and 4-bromophenol.

The experimental techniques of H (Rydberg) atom photofragment translational spectroscopy and resonance-enhanced multiphoton ionisation time-of-flight spectroscopy have been used to investigate the dynamics of H atom loss processes from gas phase 4-fluorophenol (4-FPhOH), 4-chlorophenol (4-ClPhOH) and 4-bromophenol (4-BrPhOH) molecules, following excitation at many wavelengths, lambda(phot), in the range between their respective S(1)-S(0) origins (284.768 nm, 287.265 nm and 287.409 nm) and 216 nm. Many of the Total Kinetic Energy Release (TKER) spectra obtained from photolysis of 4-FPhOH show structure, the analysis of which reveals striking parallels with that reported previously for photolysis of bare phenol (M. G. D. Nix, A. L. Devine, B. Cronin, R. N. Dixon and M. N. R. Ashfold, J. Chem. Phys., 2006, 125, 133318). The data demonstrates the importance of O-H bond fission, and that the resulting 4-FPhO co-fragments are formed in a select fraction of their available vibrational state density. All spectra recorded at lambda(phot)> or = 238 nm show a feature centred at TKER approximately 5500 cm(-1). These H atom fragments show no recoil anisotropy, and are rationalised in terms of initial S(1)<-- S(0) (pi* <--pi) excitation and subsequent dissociation via two successive radiationless transitions: internal conversion to ground (S(0)) state levels carrying sufficient O-H stretch vibrational energy to allow efficient transfer to (and round) the Conical Intersection (CI) between the S(0) and S(2)((1)pi sigma*) Potential Energy Surfaces (PESs) at larger R(O-H), en route to H atoms and ground state 4-FPhO products. The vibrational energy disposal in the 4-FPhO products indicates that parent mode nu(16a) promotes non-adiabatic coupling at the S(0)/S(2) CI. Spectra recorded at lambda(phot)< or = 238 nm reveal a faster (but still isotropic) distribution of recoiling H atoms, centred at TKER approximately 12 000 cm(-1), attributable to H + 4-FPhO products formed when the optically excited (1)pi pi* molecules couple directly with the (1)pi sigma* PES. Parent mode nu(16b) is identified as the dominant coupling mode at the S(1)((1)pi pi*)/S(2)((1)pi sigma*) CI, and the resulting 4-FPhO radical co-fragments display progressions in nu(18b) (the C-O in-plane wagging mode) and nu(7a) (an in-plane ring breathing mode involving significant C-O stretching motion). Analysis of all structured TKER spectra yields a C-F bond dissociation energy: D(0)(H-OC(6)H(4)F) = 29 370 +/- 50 cm(-1). The photodissociation of 4-ClPhOH shows many similarities, though the 4-ClPhO products formed together with faster H atoms at shorter wavelengths (lambda(phot)< or = 238 nm, by coupling through the S(1)/S(2) CI) show activity in an alternative ring breathing mode (nu(19a) rather than nu(7a)). Spectral analysis yields D(0)(H-OC(6)H(4)Cl) = 29 520 +/- 50 cm(-1). H atom formation via O-H bond fission is (at best) a very minor channel in the photolysis of 4-BrPhOH at all wavelengths investigated. Time-dependent density functional theory calculations suggest that this low H atom yield is because of competition from the alternative C-Br bond fission channel, and that the analogous C-Cl bond fission may be responsible for the weakness of the one photon-induced H atom signals observed when photolysing 4-ClPhOH at longer wavelengths.

Ultraviolet photolysis of adenine: dissociation via the 1pi sigma* state.

High resolution total kinetic energy release (TKER) spectra of the H atom fragments resulting from photodissociation of jet-cooled adenine molecules at 17 wavelengths in the range 280>lambda(phot)>214 nm are reported. TKER spectra obtained at lambda(phot)>233 nm display broad, isotropic profiles that peak at low TKER ( approximately 1800 cm(-1)) and are largely insensitive to the choice of excitation wavelength. The bulk of these products is attributed to unintended multiphoton dissociation processes. TKER spectra recorded at lambda(phot)

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of imidazole.

The fragmentation dynamics of imidazole molecules following excitation at 193.3 nm and at many wavelengths in the range of 210< or =lambda(phot)< or =240 nm have been investigated by H Rydberg atom photofragment translational spectroscopy. Long wavelength excitation within this range results in population of the 1 (1)A(")((1)pisigma(*)) excited state, but the 2 (1)A(')<--X (1)A(')(pi(*)<--pi) transition becomes the dominant absorption once lambda(phot)< or =220 nm. The measured energy disposals show parallels with those found in recent studies of the UV photolysis of pyrrole [Cronin et al., Phys Chem. Chem. Phys. 6, 5031 (2004)]. The total kinetic energy release (TKER) spectra display a "fast" feature, centred at TKER approximately 9200 cm(-1). The analysis of the structure evident in the fast feature reveals the selective population of specific in-plane stretching vibrational levels of the imidazolyl cofragment; these fragments are deduced to carry only modest amounts of rotational excitation. Comparison with calculated normal mode vibrational frequencies allows the assignment of the populated levels and a precise determination of the N-H bond strength in imidazole: D(0)=33,240+/-40 cm(-1). The observed energy disposal can be rationalized using Franck-Condon arguments, assuming that the potential energy surface (PES) for the 1 (1)A(")((1)pisigma(*)) state has a topology similar to that of the corresponding (1)pisigma(*) state of pyrrole. As in pyrrole, photoexcitation populates skeletal motions in the S(1) state (in-plane motions in the present case) that are only weakly coupled to the N-H dissociation coordinate and thus map through into the corresponding product vibrations. A second, "slow" feature is increasingly evident in TKER spectra recorded at shorter lambda(phot). This component, which exhibits no recoil anisotropy, is attributed to H atoms formed by the "statistical" decay of highly vibrationally excited ground state molecules. The form of the TKER spectra observed at short lambda(phot) is rationalized by assuming two possible decay routes for imidazole molecules excited to the 2 (1)A(')((1)pipi(*)) state. One involves fast 2 (1)A(')((1)pipi(*)) right arrow-wavy 1 (1)A(")((1)pisigma(*)) radiationless transfer and subsequent fragmentation on the 1 (1)A(')((1)pisigma(*)) PES, yielding fast H atoms (and imidazolyl cofragments)-reminiscent of behavior seen at longer excitation wavelengths where the 1 (1)A(")((1)pisigma(*)) PES is accessed directly. The second is assumed to involve radiationless transfer to the ground state, most probably by successive 2 (1)A(') right arrow-wavy 1 (1)A(") right arrow-wavy X (1)A(') couplings, mediated by conical intersections between the relevant PESs and the subsequent unimolecular decay of the resulting highly vibrationally excited ground state molecules yielding slow H atoms.

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of phenol.

The fragmentation dynamics of gas phase phenol molecules following excitation at many wavelengths in the range 279.145 > or = lambdaphot > or = 206.00 nm have been investigated by H Rydberg atom photofragment translational spectroscopy. Many of the total kinetic energy release (TKER) spectra so derived show structure, the analysis of which confirms the importance of O-H bond fission and reveals that the resulting phenoxyl cofragments are formed in a very limited subset of their available vibrational state density. Spectra recorded at lambdaphot > or = 248 nm show a feature centered at TKER approximately 6500 cm(-1). These H atom fragments, which show no recoil anisotropy, are rationalized in terms of initial S1<--S0 (pi*<--pi) excitation, and subsequent dissociation via two successive radiationless transitions: internal conversion to ground (S0) state levels carrying sufficient O-H stretch vibrational energy to allow efficient transfer towards, and passage around, the conical intersection (CI) between the S0 and S2(1pisigma*) potential energy surfaces (PESs) at larger R(O-H), en route to ground state phenoxyl products. The observed phenoxyl product vibrations indicate that parent modes nu16a and nu11 can both promote nonadiabatic coupling in the vicinity of the S0S2 CI. Spectra recorded at lambdaphot < or = 248 nm reveal a faster, anisotropic distribution of recoiling H atoms, centered at TKER approximately 12,000 cm(-1). These we attribute to H+phenoxyl products formed by direct coupling between the optically excited S1(1pi pi*) and repulsive S2(1pi sigma*) PESs. Parent mode nu16b is identified as the dominant coupling mode at the S1/S2 CI, and the resulting phenoxyl radical cofragments display a long progression in nu18b, the C-O in-plane wagging mode. Analysis of all structured TKER spectra yields D0(H-OC6H5) = 30,015 +/- 40 cm(-1). The present findings serve to emphasize two points of wider relevance in contemporary organic photochemistry: (i) The importance of 1) pi sigma* states in the fragmentation of gas phase heteroaromatic hydride molecules, even in cases where the 1pi sigma* state is optically dark. (ii) The probability of observing strikingly mode-specific product formation, even in "indirect" predissociations, if the fragmentation is driven by ultrafast nonadiabatic couplings via CIs between excited (and ground) state PESs.

Near ultraviolet photolysis of deuterated pyrrole.

High resolution time-of-flight (TOF) measurements of the D atom fragments arising in the near ultraviolet (UV) photodissociation of deuterated pyrrole are reported. Structures evident in the measured TOF spectra are all interpretable in terms of N-D bond fission, and population of selected vibrational states of the pyrrolyl-d(4) co-fragment -- thereby clarifying previous uncertainties regarding the branching into different vibronic states of the pyrrolyl radical following UV excitation of pyrrole.

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole.

The photodissociation dynamics of 2,5-dimethylpyrrole (2,5-DMP) has been investigated following excitation at 193.3 nm and at many near ultraviolet (UV) wavelengths in the range 244 < lambda(phot) < 282 nm using H Rydberg atom photofragment translational spectroscopy (PTS). Complementary UV absorption and, at the longest excitation wavelengths, one photon resonant multiphoton ionisation spectra of 2,5-DMP are reported also; analysis of the latter highlights the role of methyl torsional motions in promoting the parent absorption. The deduced fragmentation dynamics show parallels with that reported recently (B. Cronin, M. G. D. Nix, R. H. Qadiri and M. N. R. Ashfold, Phys. Chem. Chem. Phys., 2004, 6, 5031) for the bare pyrrole molecule. Excitation at the longer wavelengths leads to (vibronically induced) population of the 1(1)A(2)(pisigma*) excited state of 2,5-DMP, but once lambda(phot) decreases to approximately 250 nm stronger, dipole allowed transitions start to become apparent in the parent absorption. All total kinetic energy release (TKER) spectra of the H + 2,5-dimethylpyrrolyl (2,5-DMPyl) fragments measured at lambda(phot)> or=244 nm show a structured fast component, many of which are dominated by a peak with TKER approximately 5100 cm(-1); analysis of this structure reveals lambda(phot) dependent population of selected vibrational levels of 2,5-DMPyl, and enables determination of the N-H bond strength in 2,5-DMP: D(0) = 30 530 +/- 100 cm(-1). Two classes of behaviour are proposed to account for details of the observed energy partitioning. Both assume that N-H bond fission involves passage over (or tunnelling through) a small exit channel barrier on the 1(1)A(2) potential energy surface, but differ according to the vibrational energy content of the photo-prepared molecules. Specific parent out-of-plane skeletal modes that promote the 1(1)A(2)-X(1)A(1) absorption appear to evolve adiabatically into the corresponding vibrations of the 2,5-DMPyl products. Methyl torsions can also promote the 1(1)A(2)<-- X(1)A(1) absorption in 2,5-DMP, and provide a means of populating a much higher density of excited vibrational levels than in pyrrole. Such excited levels are deduced to dissociate by redistributing the minimum amount of internal energy necessary to overcome the exit channel barrier in the N-H dissociation coordinate. Coupling with the ground state surface via a conical intersection at extended N-H bond lengths is proposed as a further mechanism for modest translational --> vibrational energy transfer within the separating products. The parent absorption cross-section increases considerably at wavelengths approximately 250 nm, and PTS spectra recorded at lambda(phot)< or = 254 nm display a second, unstructured, peak at lower TKER. As in pyrrole, this slower component is attributed to H atoms from the unimolecular decay of highly vibrationally excited ground state molecules formed via radiationless decay from photo-excited states lying above the 1(1)A(2) state.