The bond dissociation energy (D(0)) of the water dimer is determined by using state-to-state vibrational predissociation measurements following excitation of the bound OH stretch fundamental of the donor unit of the dimer. Velocity map imaging and resonance-enhanced multiphoton ionization (REMPI) are used to determine pair-correlated product velocity and translational energy distributions. H(2)O fragments are detected in the ground vibrational (000) and the first excited bending (010) states by 2 + 1 REMPI via the C̃ (1)B(1) (000) ← X̃ (1)A(1) (000 and 010) transitions. The fragments' velocity and center-of-mass translational energy distributions are determined from images of selected rovibrational levels of H(2)O. An accurate value for D(0) is obtained by fitting both the structure in the images and the maximum velocity of the fragments. This value, D(0) = 1105 ± 10 cm(-1) (13.2 ± 0.12 kJ/mol), is in excellent agreement with the recent theoretical value of D(0) = 1103 ± 4 cm(-1) (13.2 ± 0.05 kJ∕mol) suggested as a benchmark by Shank et al. [J. Chem. Phys. 130, 144314 (2009)].
Honing in on HONO 2 Modeling air pollution requires knowledge of all the interrelated reactions occurring in the atmosphere. Among the most significant is the formation of nitric acid (HONO 2 ) from OH and NO 2 radicals. One sticking point in the study of this reaction has been the uncertainty in how often radicals link through an O-O rather than an O-N bond. Mollner et al. (p. 646 ) measured the partitioning coefficient, as well as the overall consumption rate of the radicals, with an array of highly sensitive spectroscopic techniques in the laboratory. The measurements yielded a well-defined rate constant for nitric acid formation, which was applied to the prediction of ozone levels in atmospheric simulations of the Los Angeles basin.
The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded HCl-H(2)O dimer was studied following excitation of the dimer's HCl stretch by detecting the H(2)O fragment. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the HCl stretch of the dimer, H(2)O fragments were detected by 2 + 1 REMPI via the C (1)B(1) (000) ← X (1)A(1) (000) transition. REMPI spectra clearly show H(2)O from dissociation produced in the ground vibrational state. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational states of H(2)O and were converted to rotational state distributions of the HCl cofragment. The distributions were consistent with the previously measured dissociation energy of D(0) = 1334 ± 10 cm(-1) and show a clear preference for rotational levels in the HCl fragment that minimize translational energy release. The usefulness of 2 + 1 REMPI detection of water fragments is discussed.
A joint theoretical and experimental investigation is undertaken to study the effects of OH-stretch/ HOON torsion coupling and of quantum yield on the previously reported first overtone action spectrum of cis-cis HOONO ͑peroxynitrous acid͒. The minimum energy path along the HOON dihedral angle is computed at the coupled cluster singles and doubles with perturbative triples level with correlation consistent polarized quadruple basis set, at the structure optimized using the triple basis set ͑CCSD͑T͒/cc-pVQZ//CCSD͑T͒/cc-pVTZ͒. The two-dimensional ab initio potential energy and dipole moment surfaces for cis-cis HOONO are calculated as functions of the HOON torsion and OH bond length about the minimum energy path at the CCSD͑T͒/cc-pVTZ and QCISD/ AUG-cc-pVTZ ͑QCISD-quadratic configuration interaction with single and double excitation and AUG-augmented with diffuse functions͒ level of theory/basis, respectively. The OH-stretch vibration depends strongly on the torsional angle, and the torsional potential possesses a broad shelf at ϳ90°, the cis-perp conformation. The calculated electronic energies and dipoles are fit to simple functional forms and absorption spectra in the region of the OH fundamental and first overtone are calculated from these surfaces. While the experimental and calculated spectra of the OH fundamental band are in good agreement, significant differences in the intensity patterns are observed between the calculated absorption spectrum and the measured action spectrum in the 2 OH region. These differences are attributed to the fact that several of the experimentally accessible states do not have sufficient energy to dissociate to OH+ NO 2 and therefore are not detectable in an action spectrum. Scaling of the intensities of transitions to these states, assuming D 0 = 82.0 kJ/ mol, is shown to produce a spectrum that is in good agreement with the measured action spectrum. Based on this agreement, we assign two of the features in the spectrum to ⌬n = 0 transitions ͑where n is the HOON torsion quantum number͒ that are blue shifted relative to the origin band, while the large peak near 7000 cm −1 is assigned to a series of ⌬n = + 1 transitions, with predominant contributions from torsionally excited states with substantial cis-perp character. The direct absorption spectrum of cis-cis HOONO ͑6300-6850 cm −1 ͒ is recorded by cavity ringdown spectroscopy in a discharge flow cell. A single band of HOONO is observed at 6370 cm −1 and is assigned as the origin of the first OH overtone of cis-cis HOONO. These results imply that the origin band is suppressed by over an order of magnitude in the action spectrum, due to a reduced quantum yield. The striking differences between absorption and action spectra are correctly predicted by the calculations.
The termolecular association reaction OH + NO 2 + M was studied in a low-pressure discharge flow reactor, and both HONO 2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental ν 1 band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm -1 , in good agreement with matrix isolation studies and ab initio predictions. The rotational contour of this band was partially resolved at 1 cm -1 resolution and matched the profile predicted by ab initio calculations. The integrated absorbances of the ν 1 bands of the cis-cis HOONO and HONO 2 products were measured as a function of temperature and pressure. These were converted to product branching ratios by scaling the experimentally observed absorbances with ab initio integrated cross sections for HOONO and HONO 2 computed at the CCSD(T)/cc-pVTZ level. The product branching ratio for cis-cis HOONO to HONO 2 was 0.075 ( 0.020(2σ) at room temperature in a 20 Torr mixture of He/Ar/N 2 buffer gas. The largest contribution to the uncertainty is from the ab initio ratio of the absorption cross sections, computed in the double harmonic approximation, which is estimated to be accurate to within 20%. The branching ratio decreased slightly with temperature over the range 270 to 360 K at 20 Torr. Although transperp HOONO was not observed, its energy was computed at the CCSD(T)/cc-pVTZ level to be E 0 ) +3.4 kcal/mol relative to the cis-cis isomer. Statistical rate calculations showed that the conformers of HOONO should reach equilibrium on the time scale of this exeriment. These results suggested that essentially all isomers had converted to cis-cis HOONO; thus, the reported branching ratio is a lower bound for and may represent the entire HOONO yield.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.