Intermolecular energy transfer in liquid benzene: Raman spectra, linewidth measurements, picosecond spectroscopy, and vibrational relaxation times

Abstract

A collision-induced intermolecular vibrational energy transfer process in liquid C6H6 has been studied using detailed measurements of Raman line shapes and linewidths and picosecond spectroscopy. Lifetimes of molecules in the upper vibratonal energy level of the Raman transition ν2(ν =0→1) in C6H6 and C6D6 have been evaluated using both frequency and time measurements. By varying the absolute number of C6H6–C6H6 collisions over a wide range by dilution of C6H6 with C6D6, the lifetime of the ν′2 state can be altered from 4.7−7.0×10−12 sec. The higher value corresponds to an intrinsic lifetime of ν′2 in the liquid state while the other is a lower value because of a near resonance collision induced intermolecular vibration to vibration energy transfer process which occurs in pure C6H6. Direct measurement of the ν2(a1g) vibrational lifetimes by picosecond spectroscopy gives values of 5×10−12 sec for pure liquid C6H6 and 8×10−12 sec for pure liquid C6D6.