A quasiclassical trajectory study of H+CO2: Angular and translational distributions, and OH angular momentum alignment

Abstract

We present a quasiclassical trajectory study of the H+CO2 reaction dynamics, with emphasis on product angular and translational distributions, and OH angular momentum alignment. A new potential surface has been developed for this study, based on modifications of a previously developed full dimensional empirical HCO2 potential surface. The modifications include correcting errors that cause the HO⋅⋅⋅CO dissociation barrier to be too loose, and adjusting the depth of the HCO2 minimum and the heights of several barriers, in order to bring them into agreement with their best estimates determined from ab initio calculations. We compare cross sections, energy partitioning, and mechanistic information calculated using the unmodified and modified surfaces with experimental results. Results from the modified surface improve the comparison with experiment for the product OH energy partitioning, but the product CO internal excitation is still high. The translational distributions have the same shape as measured distributions, and the average translational excitation matches some experiments but is lower than others. The angular distribution calculated at 2.6 eV on the modified surface is in good agreement with experimental results, showing both forward and backward scattered peaks, with a slight preference for backward scattering. By studying the average lifetime of the HOCO collision complex, we find that the lifetime is comparable to the rotational period so that there is considerable forward scattering (half rotation) and backward scattering (full rotation). The OH product angular momentum alignment indicates no preference for polarization of the OH rotational angular momentum vector. This result–an essentially isotropic distribution–agrees within the experimental uncertainty for measurements of OH Π(A′) polarization dependent differential cross sections and center-of-mass frame alignment parameters, but not with OH Π(A″)

Vibronic Structure of the Formyloxyl Radical (HCO2) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

“…9 However, the increased resolution afforded by SEVI allows clear separation of the main peaks as well as several weaker transitions that were not discernible in the previous study. In Figures 2 and 3, the peaks labeled A, which have "p" PAD's and are found at 28 198 and 28 362 cm -1 for HCO 2 -and DCO 2 -, respectively, correspond to the features that were previously assigned as the origin transitions to the 2 A 1 state. For HCO 2 , the origin transition to the low-lying 2 B 2 state was assigned to a feature corresponding to the small peak labeled C, with "s" PAD, at 28 516 cm -1 , and this assignment is confirmed in the work presented here.…”

“…[1][2][3][4][5] It is also a possible intermediate in the thermal decomposition of formic acid. 6,7 Formyloxyl also serves as a prototype for the more complex carboxyl free radicals such as CH 3 CO 2 , PhCO 2 , and those derived from amino acids.…”

“…The first definitive observation of the HCO 2 and DCO 2 radicals was reported in 1995 by Kim et al 9 using negative ion photoelectron (PE) spectroscopy of the formate anion, HCO 2 -. The C 2V geometry of HCO 2 -is well established, 23-27 so photodetachment of this anion provides a straightforward way to characterize the formyloxyl radical.…”

“…The C 2V geometry of HCO 2 -is well established, 23-27 so photodetachment of this anion provides a straightforward way to characterize the formyloxyl radical. Moreover, the three lowest neutral states ( 2 A 1 , 2 B 2 and 2 A 2 ) can be accessed by one electron photodetachment from the ...(1a 2 ) 2 (4b 2 ) 2 (6a 1 ) 2 molecular orbital configuration of the HCO 2 -anion. Analysis of the PE spectra established the 2 A 1 state as the ground state of HCO 2 with the 2 B 2 state lying 0.027 ( 0.015 eV (218 ( 121 cm -1 ) above.…”

“…In this paper, we report high-resolution SEVI spectra of HCO 2 -and DCO 2 -in the electron binding energy range of the 2 A 1 and 2 B 2 neutral states. The increased resolution afforded by SEVI allows the clear separation of the main peaks as well as the observation of several weaker transitions that were not discernible in the previous PE spectrum.…”