Rovibrational analysis of the absorption spectrum of HDO between 10 110 and 12 215 cm−1

Abstract

The weak absorption spectrum of monodeuterated water has been investigated between 10 110 and 12 215 cm⁻¹ by high resolution Fourier transform absorption spectroscopy with a 105 m absorption pathlength. The spectrum is dominated by the 4ν₁, 3ν₃, and ν₂ + 3ν₃ bands at 10 378.95, 10 631.68 and 11 969.76 cm⁻¹, respectively. The rovibrational assignment was performed on the basis of the ab initio calculations of Schwenke and Partridge and by using the effective Hamiltonian approach. 502 energy levels belonging to a total of 13 vibrational states were determined. The rotational structure of the (003) state is mostly isolated and could be fitted with an rms of 0.006 cm⁻¹, slightly larger than the experimental uncertainty. Most of the other levels are connected via a complex interaction scheme involving dark states which prevented a satisfactory modeling. The analysis of the rotational structure of the (013), (400) and (112) states is investigated for the first time, while the existing information for the (003) state is considerably enlarged and improved. Transitions reaching the nine other (dark) states, including the highly excited bending states, (051), (061) and (080), were detected in the spectrum as a result of intensity borrowing due to resonance interactions with bright states.