Terahertz spectroscopy of isotopic acrylonitrile

Rotational spectra of four isotopically enriched, singly substituted species of acrylonitrile have been studied up to 1.2 THz. Extensive analysis of the spectra recorded for H213CCHCN, H2CCH13CN, H2CCHC15N, and H2CCDCN, revealed the presence of the same characteristic perturbations between the ground state and the v11 = 1 excited vibrational state, that have recently been identified in the parent molecule. For this reason transitions in v11 = 1 have also been assigned in each of the four isotopic species and a coupled state analysis of g.s. and v11 = 1 was performed on a total of around 3000 lines for each species. The derived precise values of E(v11 = 1) are found to be consistent with estimates from anharmonic force field calculations. In addition, transitions for six new doubly substituted isotopic species of acrylonitrile, H213C13CHCN, H213CCH13CN, H2C13CH13CN, H213CCHC15N, H2C13CHC15N, and H2CCH13C15N, have been assigned, and their ground state spectroscopic constants have been determined. Rotational constants for all known isotopic species of acrylonitrile have been combined with ab initio calculation of vibration–rotation constants in the first evaluation of the r e SE geometry of this molecule.