To experimentally confirm the hypothesis of negative cross terms between different dephasing mechanisms, potentially leading to a broadening of the isotropic Raman line upon isotopic dilution, we present a detailed study on the concentration dependencies of all of the line shifts and widths in the four isotopic mixtures of type ${(}^{15}{\mathrm{N}}^{14}\mathrm{N}{)}_x-{(}^{14}{\mathrm{N}}_2{)}_{1-x}$, ${(}^{15}{\mathrm{N}}_2{)}_x-{(}^{14}{\mathrm{N}}_2{)}_{1-x}$, ${(}^{15}{\mathrm{N}}_2{)}_x-{(}^{15}{\mathrm{N}}^{14}\mathrm{N}{)}_{1-x}$, and ${(}^{16}{\mathrm{O}}_2{)}_x-{(}^{18}{\mathrm{O}}_2{)}_{1-x}$ near the normal boiling point of nitrogen at $T=77.35\mathrm{}\mathrm{K}$. A quite disparate behavior of the nitrogen oscillators compared to the oxygen oscillators was observed in respect to a change of their isotopic baths.

• Received 11 April 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.3850