Selective infrared excitation in D_2CO: rotational assignments and the role of collisions

Abstract

A time-resolved infrared-ultraviolet double-resonance technique is used to characterize specific rovibrational states pumped by a pulsed CO(2) laser within the nu(4) vibrational ladder of D(2)CO. The roles of rotational and quasiresonant rovibrational relaxation, requiring, respectively, < or =1 and approximately 3 gas-kinetic collisions, are studied. The rotational specificity of the latter suggests that a collision-assisted sequence of infrared absorption steps is able to account for the selective initial stages of multiple-photon excitation in formaldehyde.