Knowledge Bank

The solution spectrum of 0.025 molar HF in cyclohexane between 40 and $400cm-1$ (Datta and Barrow, J. Chem. Phys. 43, 2137 (1965) ) has been Fourier-inverted using the formulas of Gordon (J. Chem. Phys. 43, 1307 (1965) ). The decay of the rotational dipole moment correlation function to Brownian motion, calculated from the published data in this way, is seen to be oscillatory with at least one flat minimum and one maximum. The minimum, at which the direction of the permanent dipole of the HF molecule has diffused through an angle of $\pi$, occurs after $\sim 0.1\times 10-12$ sec after $t=0$; this time interval is about equal to the time needed for molecules in the most populous state $(J\sim 3)$ to rotate through an angle of $\pi$. The experimental correlation function is compared with the ones calculated for a thermal ensemble of classical, freely rotating HF molecules and for Gordon's ``m-diffusion'' model (J. Chem. Phys. 44, 1830 (1966) ).