Reflection absorption infrared spectroscopy and temperature programmed desorption investigations of the interaction of methanol with a graphite surface

Abstract

Reflection absorption infrared spectroscopy and temperature programmed desorption investigations of the interaction of methanol with a graphite surface Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Reflection absorption infrared spectroscopy ͑RAIRS͒ and temperature programmed desorption ͑TPD͒ have been used to investigate the adsorption of methanol (CH 3 OH) on the highly oriented pyrolytic graphite ͑HOPG͒ surface. RAIRS shows that CH 3 OH is physisorbed at all exposures and that crystalline CH 3 OH can be formed, provided that the surface temperature and coverage are high enough. It is not possible to distinguish CH 3 OH that is closely associated with the HOPG surface from CH 3 OH adsorbed in multilayers using RAIRS. In contrast, TPD data show three peaks for the desorption of CH 3 OH. Initial adsorption leads to the observation of a peak assigned to the desorption of a monolayer. Subsequent adsorption leads to the formation of multilayers on the surface and two TPD peaks are observed which can be assigned to the desorption of multilayer CH 3 OH. The first of these shows a fractional order desorption, assigned to the presence of hydrogen bonding in the overlayer. The higher temperature multilayer desorption peak is only observed following very high exposures of CH 3 OH to the surface and can be assigned to the desorption of crystalline CH 3 OH.

Reflection Absorption Infrared Spectroscopy and Temperature-Programmed Desorption Studies of the Adsorption and Desorption of Amorphous and Crystalline Water on a Graphite Surface

“…Hydrogen-bonded systems have previously been shown to exhibit fractional order desorption kinetics. 39,41,42 Evidence for a hydrogen bonded network within the water adlayer has also been shown in the broadness of the observed O-H stretching bands presented in the RAIR spectra (Figure 2).…”

“…The gradient of such a plot is n, the order of desorption. 39 Note that, to perform this plot, it is assumed that the desorption energy and preexponential factor do not vary with coverage or temperature. The validity of these assumptions will be demonstrated later.…”

“…39 The desorption order can be calculated using the Polanyi-Wigner equation 40 where r des is the rate of desorption, υ n is the preexponential factor of the desorption process of order n, θ is the coverage, E des is the desorption activation energy, R is the gas constant, and T s is the surface temperature. Remembering that the rate of change of coverage with respect to time (which is proportional to the intensity of the measured TPD trace, I(T)) can be linked to the rate of change of coverage with respect to temperature and that only a relative coverage, θ rel , can be obtained in the experiments described here, eq 1 becomes Rearranging and taking logarithms of this equation gives eq 3 Desorption orders, and hence a confirmation of the peak assignments, can be obtained from eq 3 by plotting a graph of ln[I(T)] Tx against ln[θ rel ] Tx at a fixed temperature, T x .…”

Thermally induced mixing of water dominated interstellar ices

“…The apparatus used for the experiments reported here has been described elsewhere, 59 hence only a brief description will be given. Experiments were performed in an ultra high vacuum (UHV) apparatus with a base pressure of r2 Â 10 À10 mbar.…”

Raman spectroscopy shows antifreeze glycoproteins interact with highly oriented pyrolytic graphite

“…New peaks were found only on certain sampling areas in the I region, and relatively thicker AFGP samples deposited from high concentrations gave fewer new peaks. Although the interaction mechanism of AFGP with HOPG needs to be clarified, the adsorption of molecules such as long n- 1 It has been reported that the long nalkane skeletal planes of monolayers of n-alkane molecules are oriented either perpendicular or parallel to the graphite (0001) surfaces; 14 CH 3 OH is physisorbed at all exposures and crystalline CH 3 OH can be formed on HOPG surface; 15 initial adsorption of AFP on a specific facet of ice can be randomly situated at first, but with high concentration of AFP, and the molecules align on the binding sites. 16 Therefore, it is reasonable to suggest that in samples deposited from low AFGP concentration, peptide backbone moiety of AFGP is parallel to the HOPG plane, while at high concentrations, the moiety is approximately perpendicular to the plane.…”