Large scale variational calculations on the vibrational level structure and vibrational mixing in S0 HDCO up to very high excitation energies

We perform converged high precision variational calculations to determine the exact energies of all vibrational states in S0 HDCO, extending up to 10 000 cm−1 of vibrational excitation energy. We also explore the resonances and intermode couplings in this energy range. We compare the calculated level structure to the recently measured frequencies by Ellsworth et al. [K.K. Ellsworth, B.D. Lajiness, J.P. Lajiness and W.F. Polik, J. Mol. Spectrosc. 252 (2008) 205] in order to check their assignments and further clarify the vibrational mixing pattern and vibrational resonances in HDCO, that are very different from the other more symmetric formaldehyde species H2CO and D2CO. For the calculations we use our specific vibrational method (recently employed for extensive vibrational studies on H2CO and D2CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure and based on the Martin, Lee, Taylor potential energy surface for formaldehyde, allowing to extend the calculations up to very high vibrational excitation energies.

Spectral structure of the 5ν2 overtone state of S0 HDCO (at 12784.3 cm−1): Overall spectrum and a detailed view of a spectral window around the central frequency of the spectrumHighlights► We perform large scale converged variational vibrational calculations on S0 HDCO. ► Calculated frequencies are compared to existing experimental data. ► We make careful assignments of the calculated frequencies and compare them to experimental assignments. ► We study theoretically the vibrational spectral structure up to very high excitation energies.