Knowledge Bank

Spectra of the $\nu 3$ band of CH$4$, CD$4$, SiH$4$ and SiD$4$ embedded in helium droplets have been obtained. Band origins and rotational and centrifugal distortion constants were acquired. Comparison of the rotational constants of normal and deuterated molecules facilitates the studying of the dependence of the effective rotational constants in helium on the molecular moment of inertia. Large differences in the rotational constants of deuterated methane and silane in helium droplets, which have very similar rotational constants in gas-phase, are ascribed to a different interaction strength of the molecules with the helium environment.