On the pure rotational spectrum of BF 3 in its vibronic ground state

The centrifugally induced pure rotational absorption spectrum of BF ₃ in its vibronic ground state has been computed using the theory of Watson. Maximum absorption of order 10 ^-5 (mol/liter) ^-1 cm ^-1 is found to occur in a frequency region around ∼30 cm ^-1. Due to the coincidence of the Q and R branches the full spectrum exhibits an intensity alternation of the individual lines which is not present in the case of T_d molecules studied previously; it could facilitate the experimental detection of the spectrum.