High-resolution FTIR spectroscopy of HNSO - Analysis of the highly perturbed v4, v6 and 2v5 bands

We report a rovibrational analysis of the v(4) and v(6) fundamentals and the 2v(5) overtone of HNSO from high-resolution Fourier transform infrared spectra. The v(6) band (out-of-plane bend) centred at 757.5 cm(-1) is c-type. The v(4) band (FINS bend) centred at 905.9 cm(-1) is predominantly a-type with a very weak b-type component (mu(2)(a)/mu(2)(b) = 12.4). Numerous global perturbations and localized avoided crossings affecting the v(4) = 1 rotational levels were successfully treated by inclusion of Fermi and c-axis Coriolis resonance terms between v(4) = 1 and v(5) = 2, and a b-axis Coriolis resonance term between v(4) = 1 and v(6) = 1. The latter term gives rise to an avoided crossing with an extraordinary vertical bar Delta K-a vertical bar = 5 selection rule. The Fermi resonance between v(4) = 1 and v(5) = 2 gives rise to strong mixing of their rotational wavefunctions in the vicinity of K-a = 18. The resultant borrowing of intensity made it possible for 2v(5) transitions in the range K-a = 16-19 to be assigned and included in a global rovibrational treatment of all three band systems. (c) 2006 Elsevier Inc. All rights reserved.