The absorption spectrum of 12C2D2 in the 10000–12500 cm−1 spectral region

Abstract

The absorption spectrum of dideuteroacetylene has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10 200–12 500cm−1 spectral region. Among 25 absorption bands of 12C2D2 rotationally analysed in this spectral region, 17 are newly observed. They include one IIu-Σ+ g and thirteen Σ+ u-Σ+ g bands starting from the vibrational ground state and eleven hot bands from the V 4 = 1 and V 5 = 1 lower states. The rotational structure of two excited levels is affected by a strongly J-dependent interaction with a perturber which induces intensity transfer to extra lines. The coupling is identified as a I-resonance interaction with δu dark states and the vibrational assignment of the perturbers is discussed. Two Σ-Σ bands of the 12C13 CD2 species, present in natural abundance in the sample, could also be identified and rotationally analysed. Most of the corresponding excited vibrational levels of 12C2D2 were unambiguously assigned using the polyad model [Herman, M., el idrissi, M. I., Pisarchik, A., Campargue, A., Gaillot, A.-C., Biennier, L., di lonardo, G. and Fusina, L., 1998, J. chem. Phys., 108, 1377] which allows vibrational energies and B V rotational constants to be predicted. In particular the previously highlighted 1/244 anharmonic resonance is confirmed by energy and intensity features in several {(V 1, V 2, V 3, V 4 = 0, V 5 = 0),(V 1 −1, V 2 + 1, V 3 V 4 = 2, V 5 = 0)} dyads. Significant deviations between predicted and experimental energy levels are observed for a few levels and discussed.