Search

This work studies the renormalization of the molecular moments of inertia IG in liquid helium. For this purpose we have measured the rotational-vibrational spectra of the ν3 modes of a series of homologous light spherical top molecules such as CH4, CD4, SiH4, and SiD4 in He droplets. The spectra were fitted to an empirical gas phase Hamiltonian, yielding a set of spectroscopic constants. We found that the additional moment of inertia, ΔIHe, scales approximately as square of IG. This is in agreement with the theoretical model which assigns ΔIHe to coupling of molecular rotation with vibration of He in the molecular vicinity. Our results also indicate a large increase in the effective centrifugal distortion constants, which is another manifestation of the interaction of the molecular rotors with the He environment. Finally, the mechanism of the relaxation of rotational energy in liquid helium is discussed. [ABSTRACT FROM AUTHOR]

Silane molecules have been embedded in helium droplets and studied via infrared laser depletion spectroscopy in the range of 2190 cm-1. We found that the R1 and Q2 lines of the ν3 band have satellites shifted by about 2.3 cm-1 towards low frequency and having similar intensity to the main lines. We assigned this perturbation in the spectrum to the coupling of the J=2 levels in ν3 and close lying ν1 vibration states. The strength of the coupling is a factor of about 50 larger in He droplets than in free molecules and have the same selection rules implied by the tetrahedral symmetry of SiH4 molecules. The perturbation, which cannot be explained within the framework of a Hamiltonian of free molecules, is evidence of strong coupling of the molecule with some He excitations in the molecular vicinity. [ABSTRACT FROM AUTHOR]

2-chloroethanol molecules having temperature from 300 to 600 K have been captured by helium droplets and the infrared spectra of the O–H and C–H stretching bands of the embedded molecules have been obtained. The intensity ratio of the bands due to trans and gauche conformers of the molecules follows the Arrhenius dependence, giving the enthalpy of conformers interconversion of 1.1 kcal/mol. It is concluded that the abundance ratio of the conformers, which are at equilibrium in the gas phase, remains unchanged upon the rapid cooling of the molecules in the helium droplets. [ABSTRACT FROM AUTHOR]

Midinfrared spectra of HCl dimers have been obtained in helium nanodroplets. The interchange-tunneling (IT) splitting in the vibrationally excited state of the bonded H–Cl stretching band (ν2) in (H35Cl–H37Cl) dimers was measured to be 2.7±0.2 cm-1, as compared to 3.7 cm-1 in free dimer. From the splitting, the strength of the IT coupling in liquid helium of 0.85±0.15 cm-1 was obtained, which is about a factor of 2 smaller than in the free dimer. The results are compared with the previous spectroscopic study of (HF)2 in He droplets as well as the theoretical study of (HF)2 and (HCl)2 dimers in small He clusters. [ABSTRACT FROM AUTHOR]