Reactions of Xe(³ P ₂) and Xe(³ P ₁) with HCl, HBr and HI; energy utilization, energy disposal, product rotational polarization and reaction dynamics

Abstract

& Agust Kvaran (1986) Reactions of Xe( 3 P 2 ) and Xe( 3 P 1 ) with HCl, HBr and HI; energy utilization, energy disposal, product rotational polarization and reaction dynamics, MolecularWe report a systematic study of the reactions of Xe(3P1, 3P2) with HCI, HBr and HI using both spectroscopic and molecular beam techniques. No reaction is observed at room temperatures for Xe(3P2) with HCI; analysis of the Xe(aPI)/HC1 data yields an estimate of the endoergicity of the 3P 2 reaction which agrees within experimental error with the threshold obtained from deconvolution of the excitation function measured in the molecular beam experiments, thus indicating little or no barrier in the entrance channel. Surprisal analysis of the vibrational population distributions obtained by inversion of the rare gas halide spectra yields estimates for the fraction of the available energy disposal into vibration (fv). The results are in broad agreement with earlier estimates and are roughly independent of the spin orbit component for a given reaction. Deviations from the purely kinematic limit in the product rotational alignment ((P2(~' 9 ~))) increase across the series HC1, HBr, HI while (f,) remains moderate, ~0"5. These results taken with the backward scattering observed for the inelastic channels at low collision energies in the Xe(3P2)/HBr system and the indication of a preferred angle of attack as evidenced by the opacity functions for this system suggest that reaction proceeds via a bent transition state lying towards the product region of the potential energy surface with an important contribution fore repulsive release of exoergicity in the exit channel. Similar trends have been observed in the analogous reactions of alkali metal atoms with the hydrogen halides.

Spin-orbit effects in gas-phase chemical reactions

“…The excimer formation channel has also been compared for Kr and Xe 3PX°a nd 3P2°r eactants. 117,187,189 The product emission spectra are fairly similar for the halide donors studied. The principal differences are an extension of the B-X spectrum to shorter wavelengths and evidence in the C-A system of greater C state product vibrational excitation for the 3P1°r eactant.…”

“…The excimer formation rate constants for the Xe 3P2°a nd 3Pi°r eactions have also been compared for several halide donors, and some variation in the ratio of these rate constants is found. 116,189 This reaction channel has also recently been studied for several of the higher excited radiating Xe(5p56p) states.107 While the 5p56p total quenching rate constants are only somewhat larger than for the metastable 5ps6s 3P2°l evel (except for NF3), the excimer product branching fractions are significantly enhanced, by a factor of ~40 in the case of HC1.107 Spin-orbit effects have also been studied for several of the nonreactive decay pathways for metastable inert gas collisions. Optical pumping state selection has been employed to compare the rate of excitation transfer (eq 13) collisions of metastable Ar(3P0°a nd 3P2°) with hydrogen atoms to yield excited H*(n = 2).…”

Angular momenta correlation in kinematically constrained reactions: application to the Ba + HI → BaI + H system

“…Indeed the study of these types of reaction constitutes one of the best examples where important kinematic factors control the scalar and vector properties of elementary chemical reactions. Among this class of reaction, the family of heavy atom plus HX (where X = halogen) processes has been studied extensively [10][11][12][13][14][15][16][17][18][19][20]. From the scalar point of view it is well known that useful information about the reaction cross-section, including its collision energy dependence, can be gained by measuring the rotational energy distribution of the product [21 , 22].…”

Dynamics of Excited Rare-Gas Atoms with Halide Molecules: The Ar(3P) + ClF → ArCl* + F, ArF* + Cl Reaction

“…Bulk experiments were performed by Setser et al., − who derived, from flowing-afterglow studies, the spectroscopic properties, the disposal of available energy into product vibration and the thermal rate constants, for reactions between metastable rare gas atoms and halide molecules (of the type MX, X 2 , and XY, where M = CH 3 , ... and X,Y = F, Cl, Br, ...). Most of the above experiments have been performed on homonuclear diatomic halogen molecules, ,,− information concerning the heteronuclear variant being less frequent. ,,− However, as will be seen below, this latter case allows for the possibility of analyzing excimer formation within competing mechanisms, thus providing, in principle, a more complex reactive process.…”