Vibrational Dynamics of Terminal Acetylenes: III. Comparison of the Acetylenic C−H Stretch Intramolecular Vibrational-Energy Redistribution Rates in Ultracold Molecular Beams, Room-Temperature Gases, and Room-Temperature Dilute Solutions

Abstract

The population relaxation rate of the first excited state of the acetylenic C−H stretch is compared for a series of isolated and solvated terminal acetylenes. The isolated molecule relaxation rate for ultracold molecules is measured using high-resolution infrared spectroscopy in a molecular beam. These measurements use a microwave−infrared double-resonance technique to obtain rotationally resolved spectra that originate in the vibrational ground state. The relaxation rates in room-temperature gas and dilute CCl4 solution (0.05 M) are measured using two-color transient absorption picosecond spectroscopy. Although the molecule-dependent contribution to the total relaxation rate in solution is proportional to the population relaxation rate measured for the isolated molecule under molecular-beam conditions, a large scale factor (27) is required to reach quantitative agreement. Part of the reason a large IVR scaling rate is observed can be attributed to the fact that the intramolecular vibrational-energy redis...