New Direct Infrared Laser Absorption Method for State-to-State Rotational EnergyTransfer in Crossed Supersonic Jets: Experimental Results and Quantum Scattering Analysis for Ar + CH4

摘要

A new method for measuring state-to-state rotational energy transfer in crossedsupersonic beams is described. The method is based on direct absorption of tunable, high-resolution infrared laser light by target molecules collisionally excited into final rotational states. The direct IR absorption approach offers high sensitivity, full quantum state resolution, a Doppler probe of final velocity components, and is applicable to any target molecule that absorbs in the near IR. Preliminary results are presented for Ar + CH4, scattering in crossed supersonic beams at a mean center-of-mass collision energy of 41 meV. Because of the high spectral resolution, the method can readily distinguish rotational fine structure states of A, F, and E symmetry in the tetrahedral group, as well as the much more energetically separated final j states. The results are compared with full quantum close-coupling calculations on two different Ar + CH4, potential energy surfaces. The state-to-state scattering results provide a sensitive measure of the potential anisotropy, and in particular probe the relative magnitudes of the different anisotropic terms in the potential (V3 and V4).... CH4, Crossed molecular beams' close coupling, High Resolution IR, Potential energy surfaces, Rotational energy transfer.