In nearly all applications of ultrafast multidimensional infrared spectroscopy, the spectral
degrees of freedom (eg, transition frequency) and the orientation of the transition dipole are
assumed to be decoupled. We present experimental results which confirm that frequency
fluctuations can be caused by rotational motion and observed under appropriate conditions.
A theory of the frequency-frequency correlation function (FFCF) observable under various
polarization conditions is introduced, and model calculations are found to reproduce the …