High‐resolution stimulated Raman spectroscopy from collisionally populated states after optical pumping (II): 13 C 2 H 2 , 13 C 12 CH 2 , 13 C 12 CD 2 and 13 C 2 D 2

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 12 C 2 H 2 and 12 C 2 D 2 (Martínez et al.). This technique has been here applied to four other isotopologues of acetylene, namely 13 C 2 H 2 , 13 C 12 CH 2 , 13 C 12 CD 2 and 13 C 2 D 2 . Transitions from the v 2 = 2 and v 4 = 2, v 5 = 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 v 2 = 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 v 2 = 1, v 4 = 2, v 5 = 1 ← v 4 = 2, v 5 = 1 band for 13 C 2 H 2 and 13 C 12 CH 2 allowed the spectroscopic characterization of the upper states. The harmonic term values and the anharmonicity constants, , and , have been derived for all the studied molecules. Copyright © 2016 John Wiley & Sons, Ltd.