Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed 13CO2 laser

Abstract

The multiphoton absorption (MPA) and decomposition (MPD) of chloroform-d induced by various 13CO2 [00°1 → 0°0] lines were studied for pressures from 0.133 to 13.3 kPa. MPA results show a cross-section increasing with pressure up to a plateau value which is likely due to rotational hole-filling. A MPA "spectrum" of the average number of photons absorbed versus wavenumber for different 13CO2 laser lines is shifted to lower wavenumbers compared to the small signal absorption spectrum by at least 5 cm−1 suggesting that a small amount of anharmonicity bottle-necking is occurring in CDCl3. A comparison of the MPD probability versus fluence for CDCl3 with that measured by other workers for fluoroform indicates that the CDCl3 is decomposed at a slightly lower fluence by an appropriate line of a pulsed CO2 laser.For the pressure range (0.2 to 4.0 kPa) and laser pulse-width used, the MPD is second order in CDCl3. The primary decomposition channel is elimination of DCl followed by reaction of CCl2 to give C2Cl2, C2Cl4, and Cl2. The DCl produced exchanges with a source of H2O in the reaction cell to give significant quantities of HCl. A post-pulse reaction between (HCl + DCl) and C2Cl2. produces (C2DCl3 + C2HCl3). Significant quantities of CCl4 are also produced by undetermined reactions.