Potential surfaces and dynamics of the O(P3)+H2O(XA111)→OH(XΠ2)+OH(XΠ2) reaction

Classical dynamics calculations are performed for O((3)P) + H2O((1)A1) collisions from 2 to 10 km s(-1) (4.1-101.3 kcal mol(-1)), focusing on product internal energies. Several methods are used to produce ro-vibrationally state-resolved product cross sections and to enforce zero-point maintenance from analysis of the classical trajectories. Two potential energy surfaces are used: (1) a recently developed set of global reactive surfaces for the three lowest triplet states which model OH formation, H elimination to make H + OOH, O-atom exchange, and collisional excitation and (2) a non-reactive surface used in past classical and quantum collision studies. Comparisons to these previous studies suggest that for H2O vibrational excitation, classical dynamics which include gaussian binning procedures and/or selected zero-point maintenance algorithms can produce results which approximate quantum scattering cross sections fairly well. Without these procedures, the classical cross sections can be many orders of magnitude greater than the quantum cross sections for exciting the bending vibration of H2O, especially near threshold. The classical cross section over-estimate is due to energy borrowing from stretching modes which dip below zero-point values. For results on the reactive surfaces, the present calculations show that at higher velocities there is an unusually large amount of product internal excitation. For OOH, where 40% of available collision energy goes into internal motion, the excited product vibrational and rotational energy distributions are relatively flat and values of the OOH rotational angular momentum exceed J = 100. Other product channel distributions show an exponential fall-off with energy consistent with an energy gap law. The present detailed distributions and cross sections can serve as a guide for future hyperthermal measurements of this system.

Section: Oh + Oh Reactionmentioning

confidence: 92%

Classical dynamics of state-resolved hyperthermal O(3P) + H2O(1A1) collisions

Braunstein

Conforti²

2013

“…The barrier height for reaction ͑13͒, E barrier ͑13͒, in the gas phase was reported to be 0.1 kcal/ mol. 34 Andersson et al 35,36 predicted that the mobility of OH radicals formed in the vacuum ultraviolet photolysis of water ice is low within the ice. However, OH radicals formed in the top 3 ML are quite mobile on top of the surface.…”

Section: 33mentioning

confidence: 99%

Formation mechanisms of oxygen atoms in the O(PJ3) state from the 157nm photoirradiation of amorphous water ice at 90K

Hama

Yabushita

Yokoyama

et al. 2009

Desorption of ground state O͑ 3 P J=2,1,0 ͒ atoms following the vacuum ultraviolet photolysis of water ice in the first absorption band was directly measured with resonance-enhanced multiphoton ionization ͑REMPI͒ method. Based on their translational energy distributions and evolution behavior, two different formation mechanisms are proposed: One is exothermic recombination reaction of OH radicals, OH + OH → H 2 O+O͑ 3 P J ͒ and the other is the photodissociation of OH radicals on the surface of amorphous solid water. The translational and internal energy distributions of OH radicals as well as the evolution behavior were also measured by REMPI to elucidate the roles of H 2 O 2 and OH in the O͑ 3 P J ͒ formation mechanisms.

“…We compared these results to our previous work which did not include the H + OOH channel 12 and to the measurements and direct dynamics modeling results of Brunsvold et al 7 For the OH+ OH channel, the present results are about a factor of 4 lower than those reported by Brunsvold et al using B3LYP density functional direct dynamics on a single surface and about a factor of 2 lower than our previous results 12 which used fitted surfaces only for the OH+ OH channel. As part of this assessment, we used variational transition state theory with the present surfaces to compute rate constants leading to OH+ OH and H + OOH, which compare favorably to available measurements.…”

Section: Global Potential Energy Surfaces For O" 3 P… + H 2 O" 1 a 1 mentioning

confidence: 45%

“…In our previous modeling of the O͑ 3 P͒ +H 2 O system, 12 we fit the three lowest triplet adiabatic potential energy surfaces leading to OH+ OH products based on ab initio electronic structure calculations. The surfaces were spline-based fits of ϳ20 000 fixed geometry ab initio calculations at the complete active space self-consistent field+ second order perturbation theory ͑CASSCF+ MP2͒ level with an O͑4s3p2d1f͒ / H͑3s2p͒ one electron basis set.…”

Section: Global Potential Energy Surfaces For O" 3 P… + H 2 O" 1 a 1 mentioning

confidence: 99%

“…To fit the ab initio points, the method of Bowman and co-workers 16,17 was used, which includes all nuclear degrees of freedom, and where the interchangeability of like-atoms is built into the functional form of the potential. 12. An overview of the surfaces addressed in the present work is shown in Fig.…”

Section: Global Potential Energy Surfaces For O" 3 P… + H 2 O" 1 a 1 mentioning

confidence: 99%

See 1 more Smart Citation

Global potential energy surfaces for O(P3)+H2O(A11) collisions

Conforti

Braunstein

Braams

et al. 2010

Global analytic potential energy surfaces for O((3)P) + H(2)O((1)A(1)) collisions, including the OH + OH hydrogen abstraction and H + OOH hydrogen elimination channels, are presented. Ab initio electronic structure calculations were performed at the CASSCF + MP2 level with an O(4s3p2d1f)/H(3s2p) one electron basis set. Approximately 10(5) geometries were used to fit the three lowest triplet adiabatic states corresponding to the triply degenerate O((3)P) + H(2)O((1)A(1)) reactants. Transition state theory rate constant and total cross section calculations using classical trajectories to collision energies up to 120 kcal mol(-1) (∼11 km s(-1) collision velocity) were performed and show good agreement with experimental data. Flux-velocity contour maps are presented at selected energies for H(2)O collisional excitation, OH + OH, and H + OOH channels to further investigate the dynamics, especially the competition and distinct dynamics of the two reactive channels. There are large differences in the contributions of each of the triplet surfaces to the reactive channels, especially at higher energies. The present surfaces should support quantitative modeling of O((3)P) + H(2)O((1)A(1)) collision processes up to ∼150 kcal mol(-1).