Coherent Raman Spectra of the v1 Mode of 10BF3 and 11BF3

Published

October 12, 2021

Author(s)

Robynne Kirkpatrick, Tony Masiello, Alfons Weber, J Nibler

Abstract

High resolution (0.001cm-1) coherent anti-Stokes Raman spectroscopy (CARS) was used to directly examine the n1 symmetric stretching mode of the planar symmetric D3h molecules 10BF3 and 11BF3. Simulations of the spectra were done using n1 rovibrational parameters deduced from published infrared hot-band and difference-band studies and the close similarity to the observed CARS spectra confirms the validity of the infrared constants. No significant perturbations by Fermi resonance or Coriolis interactions with nearby states are observed, in marked contrast to the case of sulfur trioxide, a similar D3h molecule recently studied. In the harmonic approximation, the 10BF3 and 11BF3 n1 Q-branches would be identical since the isotopic substitution is at the center of mass but, interestingly, the n1 stretching frequency for 11BF3 is found to be 0.198 cm-1 higher than for the lighter 10BF3 isotopomer. This counterintuitive result is reproduced almost exactly (0.200 cm-1) by ab initio calculations (B3LYP/cc-pVTZ) that included evaluation of cubic and quartic force constants and xij anharmonicity constants. The ab initio computations also predict to within 1% the DB, DC changes in the rotational constants in going from the ground state to the v1=1 vibrational level. The results illustrate nicely the complementary interplay of modern infrared, Raman, and ab initio methods in obtaining and analyzing rovibrational spectra.

Citation

Journal of Molecular Spectroscopy

Pub Type

Journals

Keywords

ab initio, Boron Trifluoride, Boron-10, Boron-11, CARS spectroscopy, coherent Raman spectroscopy, high resolution, rovibrational spectrum

Citation

Kirkpatrick, R. , Masiello, T. , Weber, A. and Nibler, J. (2021), Coherent Raman Spectra of the v₁ Mode of ¹⁰BF₃ and ¹¹BF₃, Journal of Molecular Spectroscopy (Accessed April 26, 2024)