High resolution infrared study of the 2nu9 and nu4 bands of 10BF2OH and 11BF2OH: Evidence of large amplitude effects for the OH- torsion -bending modes in the 9^2 and 4^1 and excited states

• Published in: Molecular physics Vol. 105; no. 13-14; pp. 1833 - 1848
• Main Authors: Perrin, Agnes, Bertseva, Elena, Flaud, J. M., Collet, David, Buerger, Hans, Masiello, Tony, Blake, Thomas
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 31.10.2007
• Subjects: Physical Sciences
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268970701426992

High resolution Fourier transform infrared spectra of gas phase BF2OH (difluoroboric acid) were recorded at Wuppertal and Richland. It was possible to perform the first rovibrational analysis of the 2nu9 (first overtone of nu9, the OH torsion) and nu4 (BOH bending) bands located at about 1043 and 961cm-1 respectively. Numerous classic vibration - rotation perturbations were observed in the analysis of the 2nu9 and nu4 bands. In addition large amplitude effects were observed for the 2nu9 and also, more surprisingly, the nu4 bands. This results in splittings of the energy levels of about 0.005 and 0.0035 cm-1 for the 9^2 and 4^1 states respectively. The theoretical model used to reproduce the experimental levels accounts for the classic vibration rotation resonances and of the large amplitude torsional (or bending) effects. The Coriolis resonances between the two torsional (or bending) substates are taken into account by {Jx,Jz} non orthorhombic terms in the v-diagonal blocks. This means that the z-quantification axis deviates from the a inertial axis by an axis switching effect of ~35 degrees for the 9^2 and of ~16.6 degrees for the 4^1 upper vibrational states. The calculation of the relative line intensities for the 2nu9 and nu4 bands accounts for these axis switching effects as well as for the intensity alternation which is due to the nuclear spin statistics since the OH large amplitude torsion and/or bending motion results indeed in an exchange of the two fluorine nuclei.