PNNL

Abstract

High-resolution infrared spectra of boron trifluoride, enriched to 99.5 atom % 11B, have been measured from 400 cm-1 to 1650 cm-1. In that region we have identified and analyzed 16 absorption bands attributed to the three fundamental bands, two combination bands, ten hot bands and one difference band. All possible states were accessed in this region through direct transitions either from the ground state or as hot bands from thermally populated levels. The spectral resolution of the measurements varied from 0.0015 cm-1 to 0.0020 cm-1. An improved set of ground state rotational constants and rovibrational constants for the infrared active fundamental vibrations have been determined from over 31,000 assigned transitions. This study resulted in the first direct characterization of the infrared inactive v1 state of 11BF3 leading to values for v1, v1B and v1C of 885.843 221(22), 0.000 505 242(26) and 0.000 678 567(55) cm-1, respectively. The Fermi resonance perturbation between the Ev3 states v3 and 3v4 (l=+1) was further elucidated by observation of hot band transitions to both the 3v4(l=+1)and 3v4(l=v3) states. Several other resonances were also found including the weak rotational interaction, between the A1v state 2v2 and the E' state of v1+v4.