Molecular dynamics of metastable atomic reactions: translational energy threshold and product rotational alignment in the reaction of Xe(³P_2,0) with CH₃Br

Abstract

Relative cross-sections for the reaction of Xe(:~P2,0) with CH3Br have been measured under crossed-beam conditions over the centre of mass t~ollision energy range 6 ~<Et~< 70 kJ tool -1. The excitation function, which qualitatively resembles that for the analogous alkali metal atomic reaction, has a clear threshold at Et=7 + 3 kJ mo1-1. A small increase in the vibrational energy of the CHaBr leads to a pronounced shift in the maximum of the translational excitation function toward lower energies. The rotational alignment in the XeBr increases slowly with Et. The results are consistent with (i) impulsive rebound dynamics, (ii) a late energy barrier in the exit channel, (iii) induced repulsive energy release with increasing collision energy.

Orientation and Alignment of Reaction Products

“…This combination permitted measurements of the product alignment as a function of the collision energy from thermal energies up to 1.25 eV. Hennessy et al (26)(27)(28)(29) studied the reactions of Xe(3P0,2) with CH3Br, CH3I, IC1, CF3 I, CC14, and BrCN and the reaction of Kr(3p0,2) with Brz in the same way, and they used simple models to assess the relative importance of kinematic and dynamic effects in the reactive scattering. Johnson et al (30) studied the reactions of Xe(3P0.2) formed in a rotor-accelerated beam with thermal gases HC1; this work was extended to include the reactions of Xe(3p0,z) with Clz and I2.…”

Vibrational population distributions from rare gas halide spectra

“…To provide further experimental support for this hypothesis we intend to use the rotor accelerated beam technique [8,9] to measure the collisional energy dependence of the branching ratios and the vibrational energy disposal in each of the competing channels. As a first stage we have developed an inversion algorithm to extract vibrational populations from the bound-free spectra which characterize the atom transfer channel.…”

“…Collisions of rare gas metastable atoms (Ar, Kr, Xe(SPz,0)) with halogens and halogen containing molecules have been much studied in the past few years and provide model systems for investigating non-adiabatic processes [1][2][3][4][5][6][7][8][9]. Reactive scattering can yield excited electronic states of the rare gas halides through atom transfer, giving rise to the oscillatory chemiluminescence spectral continua typical of bound-free transitions [1,2] Rg(SP2,o) + RX ~, RgX* + R Rg+X+hv Inelastic scattering can promote electronic excitation of the molecular collision partner leading to sensitized molecular fluorescence or more commonly dissociation Rg(aP2, 0) + RX ~Rg + RX* > RX…”

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

“…Other molecular beam experiments [5][6][7][8][9][10][11][12] determined aspects such as cross sections as a function of collision energy and product rotational alignments. 13 Bulk experiments were performed by Setser et al, [14][15][16][17][18][19][20] 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, 1,3, information concerning the heteronuclear variant being less frequent.…”

“…The analysis of the results permitted an accurate characterization of the ground and lower lying excited states of the weakly bound Rg−F* complexes. Other molecular beam experiments − determined aspects such as cross sections as a function of collision energy and product rotational alignments . 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, ...).…”