$^{83}Kr$ NUCLEAR QUADRUPOLE COUPLING IN KrHF: EVIDENCE FOR CHARGE TRANSFER

Author Institution:Rotational spectra have been observed for the $^{82}Kr$, $^{83}Kr$, $^{84}Kr$ and $^{86}Kr$ isotopes of KrHF van der Waals molecules by employing pulsed microwave Fourier transform spectroscopy in a Fabry-Perot cavity with a pulsed supersonic nozzle as the molecular source. The $^{83}Kr$ nuclear quadrupole coupling constant in KrHF has been measured in the gas phase to be $X = 10.227(71)$ MHz. using the known $^{83}Kr$ nuclear quadrupole moment, the field gradient at the Kr nucleus is interpreted in terms of the weak Kr-HF van der Waals field gradient at the Kr nucleus is interpreted in terms of the weak Kr-HF van der Waals bond. We find that the field gradient is caused partly by an HF dipole induced effect and partly by a Lewis acid type charge transfer from the Kr atom to the HF molecule. Approximately 1/200 of an electron is transferred, leading to an estimated charge transfer dipole moment of 0.08 Debye