Size-selective vibrational spectroscopy of methyl glycolate clusters: comparison with ragout-jet FTIR spectroscopy

A comprehensive experimental study of OH-stretching vibrations of size selected methyl glycolate clusters is presented. A depletion spectroscopy experiment in a crossed molecular beam apparatus was employed to scrutinize the cluster size assignment based on pressure dependence studies in a jet-FTIR experiment. First, the dimer to tetramer size assignments of the FTIR spectrum are confirmed by depletion signal angular dependencies measured at the FTIR absorption maxima. Then, independent depletion spectra of the size selected dimers through tetramers are presented. The depletion spectra exhibit peak broadening and blue-shifts with respect to the FTIR spectrum. These differences are discussed and partially explained by cluster heating through energy transfer in the scattering collisions with Ne atoms.