Vibron and roton bands in the first overtone of solid and liquid parahydrogen

The infrared spectrum of the rotovibrational band v=0{→}2 of parahydrogen has been observed in the condensed phases down to T=2 K. In the solid, phonon and roton sidebands exhibit peaks corresponding to those observed in the fundamental. Contributions arising from the reorientation of ortho-H₂ impurities have been detected. The Q₁(0)+S₁(0) band has been resolved into an asymmetric doublet, and the origin of this latter is discussed. In the liquid phase the observed line shapes include strong translational contributions, and are accounted for by assuming that at short times the excited molecule is encapsulated in the cage of nearest neighbors.