Raman stpectroscopy of vibrational and rotational relaxation of acetonitrile molecules dissolved in ionic liquids

Abstract

Vibrational and rotational relaxation processes of acelonitrile (AN)mols. as mol. probes dissolved in the imidazolium-based room-temp.ionic liq. (RTIL) 1-decyl-3-methyl-imidazolium bromide have beenstudied by Raman spectroscopy technique (the band shape anal. usingdifferent polarizations of the incident and scattered light). Ithas been shown that the vibrational relaxation processes are quickenedin the RTIL surrounding. The corresponding vibrational correlationtimes decrease from about 3 ps in the neat AN to 1.5-2 ps in AN soln.in RTIL (10 and 20 wt % of AN). The effect of RTIL environment onthe rotational dynamics of AN, namely, on the tumbling motion ofdipole moments, is rather small. However, the slow-down of AN reorientationsin RTIL was distinguished, namely, the rotational correlation timesincrease from 1.0-1.5 ps (neat AN) to 1.6-1.9 ps (AN/RTIL solns.).The results have been discussed in terms of various mol. and mediacontributions to these processes (H-bonding, highly viscous mediaeffect, intermode exchange of vibrational energy, etc). The demolitionof structural effects (short-range order and mesoscopic structuresin the nano-scale) in 1-decyl-3-methyl-imidazolium bromide by themutual penetration of AN and RTIL species is suspected. [on SciFinder(R)]