Evidence for negative cross correlations in vibrational dephasing in liquids: Isotropic Raman-line shift and width phenomena in isotopic mixtures of N-2 and O-2

To experimentally confirm the hypothesis of negative cross terms between di fferent dephasing mechanisms, potentially leading to a broadening of the is otropic Raman line upon isotopic dilution, we present a detailed study on t he concentration dependencies of all of the line shifts and widths in the f our isotopic mixtures of type ((NN)-N-15-N-14)(x)-(N-14(2))(1-x), (N-15(2)) (x)-(N-14(2))(1-x), (N-15(2))(x)-((NN)-N-15-N-14)(1-x), and (O-16(2))(x)-(O -18(2))(1-x) near the normal boiling point of nitrogen at T = 77.35 K. A qu ite disparate behavior of the nitrogen oscillators compared to the oxygen o scillators was observed in respect to a change of their isotopic baths.