A diode laser spectrometer for state-resolved experiments on the methane-surface system

A diode laser spectrometer for studying the state-resolved scattering of a molecular beam of methane in a molecule-surface system is described. Preliminary estimation of the sensitivity of the spectrometer for future scattering experiments is done. The advantages of data obtained in the 3.3 and 7.7 mu m spectral regions are analyzed. A double pulse recording scheme for the elimination of low-frequency noise in the absorption spectra of the molecular beam is proposed and tested under static conditions. Measurement of the detailed rotational vibrational distribution in a jet of methane is done to obtain the main parameters of the direct beam in scattering experiments. The rotational distribution within each vibrational polyad is found to be of Boltzmann type. A method of calculating the population for a defined vibrational state or polyad is developed to analyze the evolution of the detailed distribution during the energy relaxation under non-equilibrium conditions of the molecular jet or molecule-surface system.