A new approach for vibronic ground-state analysis of C3v molecules: Application to 12CD3H

The ground-state analysis of trideuteromethane 12CD3H is performed on the basis of all the experimental data recently assigned in the range 872–1400 cm−1, for the three bands ν3, ν5, and ν6 (with line precision of 0.002 cm−1). These data include for ν3 and ν6 about fifty “forbidden” (perturbation allowed) transitions with Δ∥K − l6∥ = ±3, allowing us to determine the pure K-dependent constants C0 and D0K, besides B0, D0J, D0JK, H0J, H0JJK, and H0JKK. The computational procedure is based on a ground-state energy calculation including all the matrix contributions within the fourth order of approximation. Thus, the two nondiagonal elements 〈J, K∥H+∥J, K ± 3〉 and 〈J, K∥H+∥J, K ± 6〉, coming from second- and fourth-order terms, respectively, are taken into account. The energies are derived by diagonalizing the energy matrix written in the basis of symmetrized functions, i.e., factorized in blocks A1, A2, E, and E. The fit of 1174 combination differences, including J″ values up to 23 and involving 69 “allowed-forbidden” or “forbidden-forbidden” relations, leads to significant values for the eight constants mentioned above with an overall standard deviation equal to 0.003 cm−1. The nondiagonal contributions appear to be nonsignificant in the present case, but their tentative adjustment points out that the H constants contribute specifically beyond the effect of nondiagonal contributions.