Asymmetric line shapes and time-resolved measurements: Vibrons in α-${\mathrm{Ar}}_{\mathit{x}}$(${\mathrm{N}}_2$${)}_{1\mathrm{-}\mathit{x}}$ mixed crystals

High-resolution Raman measurements were performed on the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}_2^{}{}_{}{}^{}$ vibrons and the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}_2^{}{}_{}{}^{}$ internal vibration in mixed crystals of α-${(}^{15}$ ${\mathrm{N}}_2$ ${)}_{0.013}$ ${(}^{14}$ ${\mathrm{N}}_2$ ${)}_{0.937}$ ${\mathrm{Ar}}_{0.05}$. In contrast to what was assumed for the analysis of previous time-resolved coherent anti-Stokes Raman-scattering measurements, asymmetric line shapes are found. We relate the asymmetry to inhomogeneous broadening resulting from perturbations of the perfect lattice structure by the Ar substitution. We discuss the consistency of these frequency-domain results with those of previous time-resolved measurements and finally show how the asymmetry is contained in the time domain.