The 4V(OH) absorption spectrum of HDO

The absorption spectrum of HDO was recorded by intracavity laser absorption spectroscopy in the 13 560-14 050 cm(-1) spectral region. Among 437 lines attributed to HDO, 399 were assigned to the 4 nu(3) highly excited overtone transition. One hundred twenty-nine experimental energy levels were derive d from the spectrum identification with rotational quantum numbers J as hig h as 16 and K-a as high as 7. The (004) vibrational state of HDO was found to be nearly isolated. Rotational and centrifugal distortion parameters of the effective rotational Hamiltonian in the Pade-Borel approximants form, r etrieved from the fitting, allow the reproduction of the experimental energ y levels with the root-mean-square deviation of 0.012 cm(-1), close to the experimental accuracy. Some rotational energy levels of the (004) state see m to be slightly perturbed by local resonances with the (052) highly excite d bending state. The resonance mixing was found to be large enough to give rise to seven 5 nu(2) + 2 nu(3) transitions, but otherwise too weak to be o bservable. The maximum difference between the derived experimental energy l evels and the recent high accuracy ab initio predictions is -2.7 cm(-1), (C ) 1999 Academic Press.