Origin of abnormally sharp features in collision-induced spectra of cryosolutionsOrigin of abnormally sharp features in collision-induced spectra of cryosolutions
Faculty of Sciences. Chemistry
2015New York, N.Y., 2015
The journal of chemical physics. - New York, N.Y.
University of Antwerp
A weak, paradoxically narrow resonance feature (shortly, the r-line) near the O2 fundamental frequency in the collision-induced absorption spectrum of oxygen dis- solved in liquid argon and liquid nitrogen (T=89 K) is resolved for the rst time. An accurate band shape tting routine to separate the r-line from the by-far more intense diffuse background and to study its behavior versus the oxygen mole fraction x which ranged from 0.03 up to 0.23 has been elaborated. At small x(.0.07 ), the r-line intensity was found to scale as x2 leaving no doubt that it is due to the solute-solute (O2􀀀O2) interactions. In line with our results on the pH2-LNe cryosystem (W.A. Herrebout et al, Phys. Rev. Lett. 101, 093001 (2008)), the Lorentzian r-line shape and its extraordinary sharpness (HWHH 1 cm􀀀1) are indicative of the motional narrowing of the relative solute-solute translational spectrum. As x is further raised, ternary solute-solute interactions impede the r-line growth in the O2-LAr spectrum because of the cancellation effect (J. van Kranendonk, Physica 23, 825 (1957)). The- oretical arguments are given that multiple interactions between the solutes should nally destroy the solute-solute induced r-line when the mixed solution approaches the limit of the pure liquid (x = 1). Interestingly, the nonbinary effects are too weak to appreciably affect the quadratic r-line scaling in the O2-LN2 cryosystem which persists up to x=0.23. It is emphasized that studies of the resonant features in the collision-induced spectra of binary cryosolutions open up unique opportunities to spectroscopically trace the microscopic-scale diffusion.