Acetylene, 12C2H2: new CRDS data and global vibration-rotation analysis up to 8600 cm−1

Abstract

The absorption spectrum of 12C2H2 has been recorded using cavity ringdown spectroscopy and analyzed in the ranges 6000 − 6356 cm−1 and 6667−7015 cm−1. Fourteen new bands have been identified and additional J-lines were assigned in 10 already known bands. These new data, together with the published vibration–rotation absorption lines of 12C2H2 accessing vibrational states up to 8600 cm−1 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l 4 + l 5 sub-states, with l i the angular momentum quantum number associated to the i degenerate bending vibration. These lines have been fitted simultaneously to spectroscopic parameters through J-dependent Hamiltonian matrices exploiting the vibrational polyad or cluster block-diagonalization, in terms of the pseudo-quantum numbers Nr = 5v 1 + 3v 2 + 5v 3 +v 4 +v 5 and Ns = v 1 + v 2 + v 3, also accounting for k and e/f parities and u/g symmetry. Modes 1 and 2 correspond to the symmetric CH and CC stretchings, mode 3 to the antisymmetric CH stretch, and modes 4 and 5 to the trans- and cis-degenerate bendings, respectively. The fit was successfully achieved, with a dimensionless standard deviation of 0.92, leading to the determination of 266 effective vibration-rotation parameters.