COHERENT SPECTROSCOPY OF ANHARMONIC MOLECULAR VIBRATIONS WHICH DISOBEY THE ALTERNATIVE FORBIDDENNESS.

A new variant of coherent spectroscopy is proposed for investigating the excitation of molecular vibration overtones which do not obey the alternative forbiddenness. Estimates obtained for the CH//4 and HC1 molecules show that the resonant susceptibility describing an optical process of the type omega //a equals 2 omega plus omega //L( omega is the frequency of infrared pumping radiation tuned to the frequency OMEGA of a molecular vibration and omega //L is the frequency of a probe beam) is considerably greater than the nonresonant ″background″ susceptibility. A distinguishing feature of this process is the absence (in an isotropic medium) of the competing process of repeated scattering of a probe beam by the fundamental harmonic of the molecular vibration.