Collision-induced radio-frequency transitions in CH3I

The highly sensitive method of radio-frequency-infrared double resonance in side a CO2 laser is applied to study collision-induced transitions in CH3I in a four-level double resonance scheme. Pure nuclear quadrupole resonances are observed as the result of collision population transfer between differ ent rotational levels. The intensity ratios of the collision-induced dips t o the corresponding three-level double resonance signals are measured for a number of transitions in the ground and excited vibrational states. Collis ion selection rules in the pure gas and in mixtures with polar and non-pola r gases are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.