An IR spectrometric investigation of the dynamic glass transition of ethanol from the rotationally disordered crystal to the orientationally disordered crystal is carried out. The samples considered are thin films formed from the gas phase at a substrate temperature of T=16K. The measurements are performed using the experimental apparatus which has been described in detail in our recent work. The sample thickness was d=2μm, and the typical rate of annealing is approximately 10K∕min. The results are compared with the phase diagram of solid ethanol proposed by M.A. Ramos et al. We observe good agreement between the temperature intervals of existence of the amorphous and crystalline states. The low-temperature amorphous phase (12–70K) is described by the present authors as amorphous solid ethanol by analogy with the amorphous solid water.
Thin films of cryovacuum condensates of ethanol-nitrogen mixtures formed by co-condensation of gas mixtures with different concentrations on a cooled metal substrate are studied by IR spectrometry. The condensation temperature was Tc = 16 K and the pressure of the gaseous phase during cryodeposition was P = 10−5 Torr. The ethanol concentration in nitrogen was varied from 0.5 to 10% and the film thickness, from 1 to 30 μm. Measurements were made in the range from 400 to 4200 cm−1. An analysis of the IR spectra and a comparison with published data shows that ethanol monomers and dimers are present in the nitrogen matrix. This is indicated by an absorption band at a frequency of 3658 cm−1 owing to vibrations of O–H bonds of ethanol monomers and dimers. The local minima of this band at 3645 and 3658 cm−1 are related to the existence of two conformational states of the ethanol molecule: anti (3658 cm−1) and gauche (3645 cm−1). In addition, the presence of ethanol dimers and monomers in the matrix leads to the appearance of absorption bands at 1259 and 1276 cm−1 attributable to deformation vibrations δ(COH) of the anti- and gauche-isomers, respectively, as well as bands corresponding to a combination of ν(CCO) valence vibrations and rotational oscillations of the methyl group r(CH3) attributable to anti-dimers (ν = 1090 cm−1) and anti-monomers (ν = 1095 cm−1). Local minima within 3000–3600 cm−1 also indicate the presence of cyclical dimers, trimers, and tetramers, as well as hexamers in the matrix. A broad band over 3250–3330 cm−1 indicates that large polyaggregates, with ethanol molecules in a hydrogen-bond state (multimer), exist in the matrix.
This article details the results of IR spectrometric studies on methanol cryovacuum condensates formed on a metal mirror at temperatures between 16–130 K. The vibrational spectra of gaseous methanol are compared to that of methanol condensed into the solid state. It is shown that the vibrational spectra have a significant dependence on the samples’ history and subsequent changes in temperature. Analysis of the obtained spectra allows for the determination of the temperature at which the glassy state (GS) transitions to the supercooled liquid (SCL) state, Tg = 102.6 K. The temperature range in which the SCL state exists is identified as 103–118 K, and the temperature range in which the SCL crystallizes, is found to be 118–120 K.
Cryogenic vacuum deposited films of nitrous oxide were studied for the following conditions: a mirror-like silver-coated copper substrate; deposition temperature 16 K; gas phase pressure during deposition 10−3 Pa. Analysis of IR-spectroscopic and thermal desorption data leads to the following conclusion. The transition from the amorphous to the crystalline state in the vicinity of 40 K proceeds in several steps that reflect the relaxation processes related to different molecular vibrations. The differences in the temperature intervals of the transitions are determined by the activation energies of the relevant vibrations. It was shown that cryocondensation at 16 K is accompanied by the appearance of flashes on the condensate surface. Based on the uniform nature of the observed processes, a model based on several possible isomorphic molecular states of nitrous oxide is suggested.
There is still no general consensus about the mechanism and nature of structural transformations in cryovacuum water ices. There are different interpretations of the behavior of the cryoprecipitates with respect to the proposed glass transition in the sequence of transformations and with respect to the values of the glass transition temperature Tg. The results of an experimental investigation of thermally stimulated polyamorphous and polymorphous transformations in cryovacuum condensed films of water ices, formed at substrate temperature 16K, are presented. The investigations are performed in the frequency interval 4200–400cm−1 using a modified cryovacuum IR spectrophotometer. A method developed by the present authors for observing the transformations of the films of the cryoprecipitates at a fixed frequency of the IR spectrometer is used. Data giving more accurate temperature intervals of the existence and transformations of different forms of amorphous solid water are obtained: high and low density and “restrained” amorphous phases and their transitions into a crystalline (cubic and hexagonal) state. It is concluded that the glass-transition temperature Tg lies in the temperature interval 136–138K. These results agree well with the results obtained by P. Jennsikens et al.
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