Dispersed fluorescence spectroscopy of S0 vibrational levels in formaldehyde-d

High resolution dispersed fluorescence (DF) spectra of excited vibrational levels in S0 HDCO up to 10 000 cm−1 energy were recorded in a free-jet expansion. Excitation to the 000 rotational level in 40 and 41 S1 HDCO yielded pure vibrational spectra that are free from rotational congestion. The 162 transitions (133 unique vibrational levels) assigned in these spectra have been fit to a multiresonant Hamiltonian model, which includes harmonic frequencies (ωi0), anharmonic constants (xij), and resonance constants (K). The assigned vibrational states were fit to the model with a standard deviation of 4.02 cm−1. Extensive vibrational mixing is observed throughout the spectra. Six harmonic constants, eight anharmonic constants, and four resonance constants (K44,1, K66,1, K44,66, and K33,5) were determined experimentally. The 18 experimentally determined spectroscopic constants, with the exception of ω10 and K66,1, were found to agree within 6 cm−1 of ab initio calculated values.