MICROWAVE SPECTRUM OF BiF

Abstract

Microwave spectral transitions of gaseous bismuth monofluoride (BiF) have been observed. The molecules were produced in a double oven system and subsequently led into the absorption cell at a temperature of $ 700^\circ$ C. Transitions $(F,^{\prime} J + 1, v)\leftarrow (F, J, v)$ with $J = 4, 6$ and 7 and $v = 0-6$ in the $0^{+}$ substate of the Hund’s case (c) $^{3}\Sigma^{-}$ ground state have been measured in the 65-110 GHz region. Analysis of the spectrum yields the following rotational and hyperfine constants: $Y_{01} = 6894.89594(84)$ MHz, $Y_{11} = -45.0474(11)$ MHz, $ Y_{21} = 81.69(45)$ kHz, $Y_{31} = 0.177(51)$ kHz, $Y_{02} = -5.5440(73)$ kHz, $eq_{e}Q(Bi) = -1150.28(12)$ MHz, $eq_{I}Q(Bi) = 4.20(12)$ MHz, $c_{Bi} = -30.0(5)$ kHz. In the Dunham constants the $Y_{1m}$ contribution due to interaction with $1^{+}$ level is included. On basis of the experimental conditions a thermodynamic value of the dissociation energy of BiF has been determined: $D_{0}^{0} (BiF) = 3.9(3) $eV. We have measured now the microwave spectra of all bismuth monohalides. It will be shown that from measurements on BiCl and BiBr information about the energy of 1-levels can be obtained.