PMC

(a) Comparison between the vibrational and rotational quenching rate coefficients for BaCl⁺ in the initial states (ν=1, j=0,1,2,3,4). The first and second numbers designate, respectively, the initial vibrational and rotational quantum number of BaCl⁺. (b) Comparison between the vibrational quenching rate coefficients of several excited rovibrational levels (ν, j) of BaCl⁺ resulting from collisions with Ca with the experimental results and with the Langevin law. The first and second numbers designate, respectively, the initial vibrational and rotational quantum number of BaCl⁺. (c) Comparison between the vibrational and rotational quenching rate coefficients for BaCl⁺ in the initial states (ν=2, j=0,1,2,5). The first and second numbers designate, respectively, the initial vibrational and rotational quantum number of BaCl⁺. (d) Comparison between the vibrational and rotational quenching rate coefficients for BaCl⁺ in the initial state (ν=3, j=2). The label of each curve designates the final vibrational level.

Decomposition of each normal vibrational mode into the contributions from six local vibrational modes for formaldehyde molecule. The labels under the x-axis are the irreducible representations and the vibrational frequencies (in cm) of normal modes. In the right panel, the decomposition result have been calibrated using experimentally measured vibrational frequencies of formaldehyde in the gas phase []. The uncalibrated calculated vibrational frequencies and decomposition result are shown in the left panel. The geometry optimization and Hessian calculation were carried out at B97XD/aug-cc-pVDZ level of theory.

T_w dependence of peaks and holes in the populations of the vibrational levels involve in the fifth order processes. As in , the green curves reflect excess population (peak), the red curves reflect reduced population (hole), and the blue curves are the sum of the peak and hole in the 1 level at each time point. Both the 2 level peak and 1 level hole give positive contributions to the 1–2 diagonal band. Vibrational relaxation in the 2 level reduces the peak by the transfer of population from the 2 to the 1 level. This transfer of population fills in the 1 level hole at the same time that vibrational relaxation in the 1 level reduces the absolute size of the 1 level hole. At some point, the 1 level peak generated from vibrational relaxation out the 2 level will exceed the size of the 1 level hole, and a net peak will exist in the 1 level (positive blue curve). At this point the 1–2 diagonal band becomes negative. The total signal from the 2 level peak and 1 level hole (blue) contributions with increasing T_w is illustrated as the black curves shown at the bottom of the figure.