Reaction pathway for the nonadiabatic reaction of Ca(4s3d 1D)+H2-->CaH(X 2Sigma+)+H

The reaction pathway and the nascent CaH product distribution in the reaction Ca(4s3d (1)D)+H(2)-->CaH(X (2)Sigma(+))+H are obtained using a pump-probe technique. The Ca atom is first prepared in the 3 (1)D state by a two-photon absorption, and then in brief time delay the laser-induced fluorescence of the reaction product CaH is monitored. The CaH(v=0,1) distributions appear to be single peaked, as characterized by Boltzmann rotational temperature of 807+/-38 K (v=0) and 684+/-77 K (v=1). The vibrational population ratio of CaH(v=0)/CaH(v=1) is determined to be 3.3+/-0.1, while the v=2 population is not detectable. The fractions of the available energy partitioning into rotation, vibration, and translation are estimated to be 0.36+/-0.05, 0.28+/-0.04, and 0.36+/-0.05, respectively. With the aid of the potential energy surfaces calculations, the current reaction should favor a near C(2v) collision configuration. The temperature dependence measurement yields a positive slope, indicative of the reaction occurrence without any potential barrier. The colliding species are anticipated to follow an attractive 1B(2) (or 2A') surface and then transit nonadiabatically to the reactive ground state surface.