Multiphoton and Multifrequency Resonances in the IR Laser Excitation of OsO₄ Molecules Cooled in a Supersonic Jet

Abstract

The three-frequency IR excitation of visible luminescence was used as the method for probing of the IR multiphoton absorption of OsO₄ molecules cooled in a supersonic jet. The first laser pulse was used to form a certain vibrational distribution below the onset of vibrational quasicontinuum. The possibility of direct excitation of the vibrational states ν = 2, 3 of pumped ν₃ mode by direct two- or three-photon absorption has been shown. The excitation spectra under the influence of the second variable laser frequency show the features attained for transitions from initially prepared vibrational levels ν = 2 or ν = 3. The dependencies of the luminescence intensity on the IR laser fluence were studied also to prove the role of the direct multiphoton transitions. The different multiphoton and multifrequency resonances were analysed in the frame of simple spectroscopic model, and appropriate anharmonicity constants were derived.