Abstract

A differentially pumped free-jet expansion, together with a waveguide CO₂ laser, has been used to measure the infrared predissociation spectrum of ethylene clusters near 950 cm^-1. The CO₂ laser has a pressure broadened tuning range of 240 MHz. We observe sharp transitions in association with many of the laser lines which activate the monomer C₂H₂ molecules in their v₇ mode. By varying the concentration of C₂H₄ in a carrier gas, by changing the carrier gas, and by using both bolometric and mass spectrometric detection systems, we are able to confirm the findings of Snels et al.¹ that there is fine structure in the ethylene dimer predissociation spectrum near 950 cm^-1. The linewidths of all the observed features lie in the 15-20-MHz range, giving a lower limit on the pre-dissociation lifetime of ~ 10ns.

© 1986 Optical Society of America