On the stability of ethanol nanoclusters in a nitrogen cryomatrix

Abstract

Investigating the processes of recondensation of ethanol molecules from a nitrogen cryomatrix onto a substrate we have previously found that the state of ethanol molecules in the matrix is not stable. A slight increase of temperature of the solid nitrogen long before its sublimation changes the vibrational spectrum of the bicomponent film ethanol-nitrogen. The results of study of this phenomenon are presented here. The measurements were carried out in the temperature range 12–40 K at the initial vacuum in the chamber of at least 10−8 Torr. The concentration of ethanol in nitrogen was from 0.5% to 3%. The methodology of obtaining the information on the state of ethanol molecules in a nitrogen matrix is based on an analysis of amplitudes of the absorption bands corresponding to vibrations of an ethanol molecule in an unbound state. In particular, the amplitude of the absorption of the strain δ(OH)-vibrations at a frequency ν = 1259 cm−1 which is a sign of the presence in this object of monomers or dimers of ethanol in the anti-conformal state was measured. On the basis of reflection spectra it is concluded that the nitrogen matrix contains poly-aggregates of ethanol formed during the condensation of a mixture of nitrogen and ethanol. A part of the ethanol molecules forming poly-aggregates is not connected by hydrogen bonds with neighboring molecules, creating in the near-surface zone of clusters an assembly of quasi-free ethanol molecules with the absorption bands corresponding to these states. An increase of temperature of the matrix leads to a decrease of the amplitude of absorption at the frequency ν = 1259 cm−1, which can be explained by the anti-gauche conversion with a corresponding decrease in the concentration of anti-component. This is confirmed by a simultaneous reduction of the amplitude of absorption of ethanol at the frequency ν = 1028 cm−1, which corresponds to vibrations of anti-conformers of ethanol. Thus, the observed decrease in the amplitude of absorption is a manifestation of reducing the number of anti- conformal states of an ethanol molecule.