Pulsed laser photodissociation of chromium hexacarbonyl at 308 nm: simultaneous monitoring of optical and acoustic emissions

Abstract

A novel, yet simple, acoustic technique was applied to measure the molar number of fragments formed in the XeCl laser-induced gas-phase photodissociation of Cr(CO) 6. The bluish-green Cr emission was also monitored and correlated with the acoustic signal. At 0.16 Torr of hexacarbonyl and for fluences below ≈ 25 mJ/cm 2, the optical signal varied as the cube of the laser fluence, in agreement with the model that highly excited Cr atoms were produced by three-photon processes. The acoustic signal y (mV) varied with fluence F (mJ/cm 2) as y = 1.77 F + 0.15 F 2, consistent with the model that most fragments were formed via two sequential single-photon processes. Both optical and acoustic signals showed onset of saturation at ≈ 25 mJ/cm 2, suggesting that single-photon photolysis was the primary Cr(CO) 6 depletion process. Quite expectedly, with a constant fluence of ≈ 20 mJ/cm 2 and varying hexacarbonyl pressure, the optical and acoustic signals were linearly correlated.