Anharmonicity and hydrogen bonding. III. Analysis of the near infrared spectrum of water trapped in argon matrix

The infrared spectra of H-2 O-16 and H-2 O-18 trapped in solid argon were recorded in the range 8000-15 cm(-1) at Ar/H2O molar ratios between 2000 and 20. At low concentration in water the quasifreely rotating monomer predominates, giving rise to relatively narrow rovibrational signals for the transitions involving exclusively the J = 0 and I rotational levels, i.e. the R(0)-, Q(I)- and P(l)-type transitions. For the dimer most of the one and two quanta transitions of both proton acceptor (PA) and proton donor (PD) subunits were identified on the basis of O-16/O-18 isotopic substitution and of the results previously obtained in nitrogen matrix [Chem. Phys. 266 (2001) 109]. A new assignment for v, of PA is proposed, involving the internal rotation of PA around its symmetry axis, as observed in the gas phase and in He clusters. As in N-2 matrix the 2v(1) band of PD has not been observed, which confirms the intensity weakening of the first overtone of a hydrogen-bonded OH oscillator (OHb). The same phenomenon occurs for larger polymers (H2O)(n), n > 2. The data analysis is focused on three points: rovibrational analysis and determination of the rotational parameters of some A(1) vibrational levels; role of Fermi resonance as shaping mechanism of the vOH(b) band of water polymers; determination of electrooptic parameters from intensity measurements for both monomer and dimer. (C) 2001 Elsevier Science B.V. All rights reserved.