Experimental investigation of the rotational- and vibrational-state dependence of the HF–Rg interactions

Abstract

A systematic investigation of the rotational- and vibrational-state dependence of the HF-Rg (Rg = He, Ar, Kr, Xe) intermolecular interactions has been performed using the technique of light-induced drift. Data are presented of the relative change in collision rate upon excitation Δν/ν≡(νe−νg)/νe of HF with respect to Rg. We studied the P- and R-branch of the fundamental vibrational band (v=0→1) with the rotational quantum number J ranging from J=0 through 6 using a continuously tunable F-Center Laser (λ≊2.5 μm). The results indicate that v and J have independent additive influences upon the collision rate ν. This allows one to determine the v- and J-dependence of ν separately. It is found that, upon vibrational excitation v = 0 → 1, ν increases by ≊0.15% for HF-He; ≊1.0% for HF-Ar, Kr and ≊1.5% for HF-Xe. A remarkable J-dependence of ν is observed: for HF-Ar, Kr and Xe, the collision rate ν first decreases by ≊5% for J=0→1, subsequently reaches a minimum for J=2 and then increases again for higher J. By contrast, for HF-He, ν decreases monotonically for J=0 through 5 by ≊ 4%. The influence of the optically induced alignment of J is found to produce a minor contribution only.

Spectroscopy of HF and HF-Containing Clusters in Solid Parahydrogen

“…Spectroscopy of HF and its clusters has been extensively investigated in both experimental − and theoretical works. − This is because HF molecules provide a prototype for hydrogen-bonded systems. In particular, HF dimers as one of the simplest systems have attracted the greatest interest. − ,− Hydrogen bond interconversion of dimers causes the tunneling splitting in their spectra and has been considered as one of the primary processes of cluster dynamics .…”

“…HF monomers, polymers, and clusters with other species in condensed phases have been also studied in many works. − Infrared absorption spectra of the monomer and polymers, and HF-N 2 , HF-H 2 , HF-O 2 , etc., in solid Ar and solid Ne were reported previously. − The matrix isolation technique has been a useful method for spectroscopy of unstable molecules including radicals and clusters. , However, strong interactions with rare gas matrices make it difficult to perform a high resolution spectroscopy and detailed studies of subtle interactions and dynamics in solids.…”

“…Quantum matrices such as solid p H 2 − and helium nanodroplets − , are proven to be excellent environments for the high-resolution spectroscopy of cold molecules. In general, molecules embedded in these quantum matrices exhibit quantized rotational states and extremely long lifetimes of vibration–rotation excited states, which makes the line widths of the rovibrational transitions of molecules narrow in these quantum matrices.…”

“…In general, molecules embedded in these quantum matrices exhibit quantized rotational states and extremely long lifetimes of vibration–rotation excited states, which makes the line widths of the rovibrational transitions of molecules narrow in these quantum matrices. Furthermore, the small cage effect of solid p H 2 allows us to use it as a reaction field and study chemical reactions at low temperature, including tunneling-reactions. − He nanodroplet studies in combination with the pendular spectroscopy performed by R. E. Miller et al − revealed the structure and dynamics of HF monomers, polymers, and clusters with other species in the superfluid helium environment. Their time scale to trace the dynamics was limited in the millisecond range.…”

Rotational quenching of dipole-dipole interaction

“…When averaging over the initial M i , some care should be taken in view of the anisotropy ("alignment") induced by laser excitation. Since its effect on the experimental results has been shown to be small [10], [13], we will ignore this and assume an isotropic distribution. Because of the orthonormality of the tensor T 1σ , the double summations reduce to single ones.…”