About cookies on this site Our websites require some cookies to function properly (required). In addition, other cookies may be used with your consent to analyze site usage, improve the user experience and for advertising. For more information, please review your options. By visiting our website, you agree to our processing of information as described in IBM’sprivacy statement. To provide a smooth navigation, your cookie preferences will be shared across the IBM web domains listed here.
Publication
Physical Review A
Paper
Collision-induced optical double resonance
Abstract
In a previous paper, we demonstrated that a set of new resonances can accompany the conventional infrared Lamb-dip or double-resonance transitions in CH3F gas. These satellite lines have a different origin from the primary resonances even though they are similar in intensity and linewidth. The traditional double resonance, for example, requires that a molecule interact simultaneously with two radiation fields, causing a transition from an initial to a final state through an intermediate level. Here, the double-resonance concept is extended to the situation of two coherently driven optical transitions that do not share a common level but are coupled by molecular collisions that tip the angular momentum vector while preserving the molecular velocity and rotational energy. Thus, velocity-selective population changes are communicated from one transition to another through collisions. Collision-induced double resonance is observed with Stark tuning as a series of sharp lines, free of Doppler broadening and can be explained in the same order of perturbation theory as the ordinary double-resonance experiment. Each satellite corresponds to a specific level structure involving one or more collision-induced transitions among the space-quantized M states. Virtually all characteristics of these satellite resonances, either in Lamb-dip or double-resonance experiments, are in agreement with the theory presented. While purely optical coupling mechanisms can yield double-resonance behavior also, such effects are estimated to be too weak. For the symmetric top molecule CH3F, the dipole-dipole interaction of collision pairs dominates and induces the observed reorienting transitions. The corresponding cross section for low-angular-momentum states (J,K=4,3 or 5,3) is found to be 100 A2 whereas for high-angular-momentum states (J,K=12,2), the cross section is calculated to be about 100 times smaller, and satellite resonances are not even detected. A treatment is presented also for the case where the collisionally coupled M states require a sequential transfer of population over intermediate levels. The problem of velocity smearing is discussed in this context where the energy exchange in a collision is small and also for more energetic collisions that may involve rotational quantum jumps. © 1974 The American Physical Society.