High‐resolution stimulated Raman spectroscopy from collisionally populated states after optical pumping (II): 13C2H2, 13C12CH2, 13C12CD2 and 13C2D2

The combined use of a pump-probe Raman–Raman technique and the naturally occurring process of vibration-to-vibration collisional relaxation to populate and obtain high-resolution Raman spectra of vibrationally excited states that cannot be easily accessed by other means has been recently demonstrated in 12C2H2 and 12C2D2 (Martinez et al.).[1] This technique has been here applied to four other isotopologues of acetylene, namely 13C2H2, 13C12CH2, 13C12CD2 and 13C2D2. Transitions from the v2 = 2 and v4 = 2, v5 = 1 collisionally populated states have been observed. The latter state was accessible only in the case of hydrogenated molecules. Accurate values of the spectroscopic parameters for the v2 = 3 vibrationally excited states for all the isotopologues were obtained, for the first time, from the least-squares analysis of the assigned transitions. In addition, the observation of Q branch lines of the v2 = 1, v4 = 2, v5 = 1 ← v4 = 2, v5 = 1 band for 13C2H2 and 13C12CH2 allowed the spectroscopic characterization of the upper states. The harmonic term values and the anharmonicity constants, ω20, x220 and y2220, have been derived for all the studied molecules. Copyright © 2016 John Wiley & Sons, Ltd.