Nonstatistical CO product distributions from the hot H-atom reaction, H+CO2→OH+CO

Abstract

A quasiclassical trajectory study of the OH+CO reaction J. Chem. Phys. 95, 1635 (1991); 10.1063/1.461076 Investigation of OHH2 and OHCO reactions using argonsensitized pulse radiolysisThe hot H-atom reaction, H + e0 2 ..... OH + eo is investigated under several initial conditions designed to vary the angular momentum of the CO 2 reactant. The translationally hot H atoms are produced by photodissociating H 2 S at 193 nm, resulting in a reaction exoergicity of -120 kJ mol -1. The internal energy in the eo product is monitored by laser-induced fluorescence in the VUV spectral range. Under near-nascent conditions we report the rotational distributions of eo in v" = 0 under e0 2 reactant "temperatures" of 300, 70 and 40 K. Also reported are the rotational distributions of eo in V" = 1 at 300 K and 70 K and the population ratios of [v" = 1 ]I [v" = 0] at both initial CO 2 temperatures. Three distinctively "dynamical" aspects of the potential energy (PE) surface are exhibited in this set of experiments: (i) As the CO 2 reactant is cooled, a cooling of the eo distribution is seen which suggests the reaction intermediate does not live long enough to randomize its internal energy. (ii) We report a coupling of vibrational and rotational excitation in the CO product indicated by a "hotter" rotational energy in v" = 1 than v" = 0 at 300 K. (iiifln addition, we report different [v" = 1] / [v" = 0] ratios at the two CO 2 initial temperatures. eontrary to nearly all indications from measurements on the OH product, the CO product is rich in "nonstatistical" behavior.

An Experimental Study of the Dynamics of the Reaction H + CO2 → OH(v‘, j‘, f) + CO: Product State-Resolved Differential Cross Sections and Translational Energy Release Distributions

“…(The phase space theoretical population distributions were calculated using a maximum orbital angular momentum L max ∼ 100 ℏ, but were found insensitive to L max in range ∼10−100 ℏ). Since f t = 1 − (where is the fraction of the energy available for the CO coproducts of OH( v ‘ = 0, N ‘ = 1) which is released into CO internal excitation), the data reveal that the pair-correlated CO internal energy distributions at both collision energies are considerably colder than phase space theory prediction, a conclusion which is in general accord with the (OH state-averaged, global) CO internal state populations determined by Rice and Baronavski . The results are also consistent with our previous measurements of the internal energy distribution of the CO coproducts of OH( v ‘ = 0, N ‘ = 5, A ‘/ A ‘‘), generated via reaction 1 at 2.5 eV …”

Quasi-classical trajectory study of the H + CO2 → HO + CO reaction on a new ab initio based potential energy surface

“…We have also calculated the rotational state distributions of CO with thermally prepared CO 2 (data not shown) and found no significant differences, in contrast to what observed by Rice and Baronavski. 15 In addition, the calculated CO rotational state distributions on the ground and first excited CO vibrational channels are quite similar. This is consistent with the observation of Nickolaisen et al, 16 but differ from the report of Rice and Baronavski, 15 who observed high rotational excitation for v = 1.…”

“…For instance, the latest QCT study 34 on the Lakin-Troya-Schatz-Harding (LTSH) PES (Ref. 30) failed to reproduce the monotonically increasing excitation function observed in the experiment of Hoffmann et al 14 In addition, this theoretical study predicted much hotter CO rotational state distributions than observed experimentally by Rice and Baronavski 15 and by Nicholaisen et al 16 A key issue in reaction dynamics is the accuracy of the underlying PES. The HOCO PES is quite complex, involving two bottlenecks along its main reaction pathway, as shown in Fig.…”

“…6, where the available experimental data 15,16 and our results on the LTSH PES at 1.86 and 2.35 eV are also included for comparison. It can be readily seen that our calculations found a much more highly excited rotational degree of freedom for the CO product in both the v = 0 and 1 channels than the experimental data.…”

“…The thermal rate constants for the title reaction indeed exhibit a clear Arrhenius behavior, 6,7 but are much smaller than its inelastic counterpart. 8 The subsequent research has focused on the cross sections and product distributions, [9][10][11][12][13][14][15][16][17] and multiple non-statistical features have been found for the reaction. More recently, attention has shifted to state-to-state reaction dynamics, [18][19][20][21] revealing surprisingly complex and rich dynamics.…”