Product multiplet branching in the O(1D)+H2→OH(2Π)+H reaction

Abstract

The statistical model of atom-diatom insertion reactions is combined with coupled-states capture theory and used to calculate product multiplet-resolved integral cross sections for the title reaction. This involves an ab initio determination of the four electronic potential energy surfaces that correlate with the products ((1,3)A(') and (1,3)A(")), and an accurate description of the electronic and spin-orbit couplings between them. The dependence of the resulting cross sections on the final-state rotational quantum number shows a statistical behavior similar to that observed in earlier studies of the reaction in which only the lowest ((1)A(')) potential was retained. In addition, however, the present calculations provide information on the branching between the OH((2)Pi) multiplet levels. Although the two spin-orbit manifolds are predicted to be equally populated, we find a strong propensity for the formation of the Pi(A(')) Lambda-doublet states. These two predictions confirm the experimental results of Butler, Wiesenfeld, Gericke, Brouard, and their co-workers. The nonstatistical population of the OH Lambda-doublet levels is a consequence of the bond breaking in the intermediate H(2)O complex and is preserved through the multiple curve crossings as the products separate. This exit-channel coupling is correctly described by the present theory.

The non-statistical dynamics of the 18O + 32O2 isotope exchange reaction at two energies

“…The only significant difference in the modified ("slow") 18 O atomic beam from the "fast" 18 O atomic beam was the slower average velocity of 1887 m/s (compared to 2170 m/s). The speed ratios for the slow and fast 18 O beams were not significantly different (25 and 28, respectively), however, and the angular divergences were identical (± 4.5 FWHM to best cover the center-of-mass (COM) angular range of scattering for the v = 1 channel of the product 34 O 2 only since the large background in the v = 0 backward scattering region prohibited sampling that would be sufficient to distinguish differences in the angular distribution of the v = 0 channel from that in the 7.3 kcal/mol experiments (which also showed a large uncertainty in the backward scattering region). Newton diagrams (Figures 2 and 3) demonstrate that at both collision energies the backward scattering region for v = 0 was close to the 32 O 2 beam at 90.…”

“…Therefore, the peak of the backward scattering region was experimentally inaccessible since the large background from natural abundance 34 O 2 (0.4%) in the unlabeled O 2 beam overwhelmed the signal at angles greater than 60. We note, however, that the 7.3 kcal/mol experiments were not fully blind to backward scattering from the v = 0 channel since the v = 0 TOF peak had significant width that extended all the way to the v = 1 peak (see Van Wyngarden et al 15 ).…”

A Comprehensive Study of Infrared OH Prompt Emission in Two Comets. II. Implications for Unimolecular Dissociation of H2O

“…Preferential population of Å(A 0 ) states has also been observed for dissociation of water initiated by the chemical reaction ( Butler et al 1986;Cleveland et al 1987;Alexander et al 2004 (Harich et al 2000). Calculations by Dixon (1995) and Dixon et al (1999) addressing these dissociation channels imply that for slow molecular rotation of H 2 O, the Å (A 0 ) states dominate, with the effect being strongest in the limiting case of the nonrotating parent.…”

An Important Well Studied Atmospheric Reaction, <mml:math altimg="si1.gif" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.elsevier.com/xml/ja/dtd" xmlns:ja="http://www.elsevier.com/xml/ja/dtd" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:tb="http://www.elsevier.com/xml/common/table/dtd" xmlns:sb="http://www.elsevier.com/xml/common/struct-bib/dtd" xmlns:ce="http

“…Recently, Alexander et al [29] carried out an ab initio study of the four states (X 1 A ,Ã 1 A ,ã 3 A andã 3 A ) that correlate to OH-H in the product region and the electronic and spin-orbit couplings between them. These PESs were used to study the nonadiabatic effects on the branching between the product OH ( 2 Π ) multiplet levels, using a statistical model of atom-diatom insertion reactions combined with coupled-states capture theory.…”

“…Numerous theoretical studies of its dynamics have also been carried out, for example see [11,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], using several potential energy surfaces (PESs) published for this system [29,[32][33][34][35][36][37][38][39][40][41][42][43]. These works have been the subject of partial reviews by Liu [44], Althorpe and Clary [45], Balucani et al [46] and Aoiz et al [47].…”