Fast and exceptionally slow vibrational energy transfer in acetylene and phenylacetylene in solution

Abstract

The excitation of the CH-stretching mode (ν3) of C2H2 in CCl4 leads to fast population (<2 ps) and very slow depopulation (240 ps) of the symmetric CC-stretching mode (ν2). The long lifetime of ν2 is due to the absence of anharmonic interaction to neighboring states (symmetry forbidden). The corresponding CC-stretching mode of C6H5–C2H has a lifetime of 15 ps. The phenyl group relaxes the symmetry restrictions and introduces new decay channels.