Knowledge Bank

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) $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$ ground state have been measured in the 65-110 GHz region. Analysis of the spectrum yields the following rotational and hyperfine constants: $Y01=6894.89594(84)$ MHz, $Y11=-45.0474(11)$ MHz, $ Y_{21} = 81.69(45)$ kHz, $Y31=0.177(51)$ kHz, $Y02=-5.5440(73)$ kHz, $eqeQ(Bi)=-1150.28(12)$ MHz, $eqIQ(Bi)=4.20(12)$ MHz, $cBi=-30.0(5)$ kHz. In the Dunham constants the $Y1m$ 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.