Rotationally resolved infrared-ultraviolet double resonance spectroscopy in molecular D 2CO and HDCO

Abstract

Rotationally resolved infrared-ultraviolet double resonance (IRUVDR), consisting of sequentially excited rovibrational and rovibronic transitions sharing a common intermediate molecular level, is demonstrated. The technique employs pulsed CO 2 and tunable dye lasers and is applied to the molecules D 2CO and HDCO. For D 2CO, infrared pumping produces 100fold population enhancement in specific rotational sublevels of the v 4 = 1 level of the X ̃ 1A 1 electronic ground state, followed by ultraviolet excitation in the 365-nm 4 1 0 band of the A ̃ 1A 2 ← X ̃ 1A 1 electronic system. This ultraviolet excitation occurs at a specific set of dye laser frequencies, determined by the preceding rovibrational transition, and is detected by molecular fluorescence in the visible region. Similar effects observed in HDCO involve rovibrational pumping to either the v 6 = 1 or v 5 = 1 levels and give rise to enhanced rovibronic transitions in the 6 1 0 and 5 1 0 bands of the A ̃ ← X ̃ system, respectively. The resulting IRUVDR spectra enable detailed spectroscopic assignments to be made and are consistent with previous results from infrared and ultraviolet absorption, laser Stark, and infrared-radiofrequency double resonance spectroscopy. Collision-induced satellite structure, arising from rotational relaxation of the intermediate rovibrational level in the IRUVDR sequence, is also reported.