Collisional energy transfer in highly vibrationally excited H₂CO( ¹A₁)

You are not logged in to this journal. Log in

Collisional energy transfer has been investigated in highly vibrationally excited H₂CO ( ¹A₁) at E_vib11 400 cm⁻¹ using the method of stimulated emission pumping–transient absorption spectroscopy (SEP-TAS). Total depopulation and state-to-state rate constants were measured for several rotational levels of the 2₄4₄ vibrational state. For H₂CO self-relaxation the depopulation rate constant of the 6_1,5 level was measured to be k₀=(3.12±0.13)×10⁻⁹ cm³/molecule s. An analysis of the state-to-state data with a simplified master equation approach yielded rate constants k₁=(7.7±1.2)×10⁻¹⁰, k₂=(1.2±0.3)×10⁻¹⁰, and k₃=(0.6±0.3)×10⁻¹⁰ cm³/molecule s for collisions with J=1, 2, and 3, respectively, and K_a=0, K_c=J, the reverse rate constants being given by microscopic reversibility. Thus, the J=±1 steps account for ~50% of all inelastic collisions, which can be rationalized in terms of a simple dipole–dipole interaction. At E_vib11 400 cm⁻¹, where _vib0.42/cm⁻¹, collisions seem to conserve the vibrational character in spite of the fact that the energy gap between adjacent vibrational states is a fraction of the transferred rotational energy. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.