Selective vibrational excitation of formaldehyde X 1A1 by stimulated emission pumping

Abstract

Stimulated emission pumping (SEP), an optical–optical double resonance scheme whereby highly excited rotation-vibration levels of the electronic ground state may be selecetively populated, is applied to formaldehyde. This method is free of important limitations of other schemes such as IR multiphoton, high overtone, and stimuated Raman pumping. We report fully resolved, assigned, and sub-Doppler (laser linewidth limited to 0.04 cm−1) SEP spectra in the H2CO Ã 1A′′–X̃ 1A1 441 and 230401 bands. More than 0.02% of the total thermal population in the irradiation volume was excited into a single rotation-vibration level at least 4600 cm−1 above the vibrationless level in the electronic ground state.