The vibrational energy pattern in propyne (12CH312C2H) Original Research Article

The results of ab initio calculations at the MP2 level of theory are presented, which provide refined equilibrium geometrical parameters and better characterization of the vibrational normal modes in propyne (CH3C2H). These results help performing the vibrational analysis of the high resolution Fourier transform absorption spectrum of this molecule which has been recorded between 2000 and 10 200 cm−1. The vibrational assignment criteria also include, in particular, the detailed identification of the band shape based on the observed rotational structure that is resolved for most bands. Some 46 bands are observed and their band shape identified in most cases. Among the bands newly reported, some 14 are vibrationally assigned, three of them tentatively. The relative intensity of all observed bands is estimated from the spectra. Approximate ζ rotational constants are obtained for ν3+ν6 (0.074) and 2ν1+ν8 (0.38). The results are merged with those of the previous literature, leading to list the origin of 118 vibrational bands, from which an extensive set of vibrational constants is extracted. Two polyad quantum numbers emerge from the vibrational energy pattern: Nsb=3v1+v3+2v5+v9 and Ns=v1+v3, supported by the ν1 with ν3+ν5 and ν1 with ν3+2ν9 anharmonic resonances.