Quantum State-Resolved Energy Transfer Dynamics at Gas-Liquid Interfaces: IR Laser Studies of CO^d2 Scattering from Perfluorinated Liquids
B G. Perkins, David Nesbitt
An apparatus for detailed study of quantum state resolved inelastic energy transfer dynamics at the gas-liquied interface is described. The approach relies on supersonic jet cooled molecular beams impinging on a continually renewable liquid surface in vacuum, exploiting sub-Doppler high resolution laser absorption methods to probe rotation, vibration and translational, distributions in the scattered flux. First results are presented for skimmed beams of jet cooled CO2(Tdbeam^15 K) colliding at normal incidence witha liquid perfluoropolyether (PFPE) surface at Einc = 11 kvsl/mol, with tunable Pb-salt diode laser direct absorption on the COd2 3 asymmetric stretch. Measured rotational distributions in both 0000 and 01^10 vibrational manifolds indicate CO2 inelastically scatters from the liquid surface into a clearly non-Boltzmann distribution, indicating non-equilibrium dynamics with average rotational energies in excess of the liquid (Tds=300 K). Furthermore, high resolution analysis of the absorption profiles reveals Doppler widths correspond to temperatures significantly warmer than Ts and increase systematically with J rotational state. These rotational and translational distributions can be reconciled with the presence of two distinct collision pathways, (i) a T 300 K component due to trapping-desorption (TD) events, and (ii) a much hotter distribution (T 750 K) due to prompt direct impulsive scattering (IS) from the gas-liquid interface. In constant vibrational populations in the COd2 bending mode are inefficiently excited by scattering from the liquid, which is consistent with much slower T-V collisional energy transfer.
and Nesbitt, D.
Quantum State-Resolved Energy Transfer Dynamics at Gas-Liquid Interfaces: IR Laser Studies of CO^d2 Scattering from Perfluorinated Liquids, Journal of Physical Chemistry
(Accessed February 29, 2024)