Influence of vibrational excitation on the nonadiabatic reactions of metal atoms with H2

Abstract

The reactions of alkaline earth metal atoms, Mg(3s3p 1P1) and Ca(4s4p 1P1), with H2(v = 1, j) are studied using a pump-probe technique combined with stimulated Raman pumping and coherent anti-Stokes Raman spectroscopy. For the Ca(4 1P1) case, the energy deposited in the v = 1 level enlarges the H2 bond distance to help facilitate the reaction without opening an additional pathway. For the Mg(3 1P1) case, the vibrational excitation of H2 leads to enhancement of the low rotational component of the rotational distribution and the MgH(v = 0)/MgH(v = 1) ratio. These results can be predicted with quasi-classical trajectory calculations and interpreted with a kinematic collision model.

Dynamical and stereodynamical studies of alkaline-earth atom–molecule reactions

“…Like this case, the vibrational excitation of H 2 helps open up new reaction pathways in the reactions with C( 1 D) and O( 3 P) [53,54] or increased rotational excitation of HD (v ¼ 1) in the reaction with D [25,55]. An active focus to find how energy is deposited and released was carried out in the Mg(3p 1 P) þ H 2 (v ¼ 1) reaction [24]. Hydrogen molecules in v ¼ 1, j ¼ 0-3 are prepared by using stimulated Raman pumping (SRP) [22][23][24][25][52][53][54][55].…”

“…The population fraction in the v ¼ 1 level is estimated to be 7.5% by using coherent anti-Stokes Raman spectroscopy [22][23][24]. As shown in figure 8, vibrational excitation of H 2 leads to enhancement in the low-N …”

“…The fraction of population in the vibrational excitation can be estimated by using either Coherent antiStokes Raman spectroscopy (CARS) [22][23][24] or resonance-enhanced multiphoton ionization (REMPI) [25]. Following photolysis of a metal-containing molecule, it is possible to acquire polarization-dependent Doppler-resolved LIF spectra of the products when the resulting fast metal atoms react with a collision partner in a gas chamber.…”

“…An active focus to find how energy is deposited and released was carried out in the Mg(3p 1 P) þ H 2 (v ¼ 1) reaction [24]. Hydrogen molecules in v ¼ 1, j ¼ 0-3 are prepared by using stimulated Raman pumping (SRP) [22][23][24][25][52][53][54][55].…”

“…The Ca(4p 1 P) þ H 2 (v ¼ 1) reaction was further conducted to confirm the proposed reaction pathway. The H 2 v ¼ 1, j ¼ 0-3 level was excited using stimulated Raman pumping, while the fraction of vibrational population in this level was determined to be 7.5% out of the total vibrational population by using coherent anti-Stokes Raman spectroscopy (CARS) [22][23][24]. As shown in figure 10, the resulting CaH(v ¼ 0 and 1) rotational distributions obtained by the H 2 (v ¼ 1) reaction appeared to be similar to those by H 2 (v ¼ 0) reaction, but the CaH product yield (or the reaction cross-section) was enhanced by an order of magnitude.…”