Issue 43, 2020

A new technique for determining the refractive index of ices at cryogenic temperatures

Abstract

A reflection–absorption optical (RAO) spectrometer, operating across the ultra-violet/visible (UV/visible) wavelength region, has been developed that allows simultaneous measurements of optical properties and thickness of thin solid films at cryogenic temperatures in ultrahigh vacuum. The RAO spectrometer enables such measurements to be made after ice deposition, as opposed to most current approaches which make measurements during deposition. This allows changes in the optical properties and in the thickness of the film to be determined subsequent to thermal, photon or charged particle processing. This is not possible with current techniques. A data analysis method is presented that allows the wavelength dependent n and k values for ices to be extracted from the reflection–absorption spectra. The validity of this analysis method is shown using model data from the literature. New data are presented for the reflection UV/visible spectra of amorphous and crystalline single component ices of benzene, methyl formate and water adsorbed on a graphite surface. These data show that, for benzene and methyl formate, the crystalline ice has a larger refractive index than amorphous ice, reflecting changes in the electronic environment occurring in the ice during crystallisation. For water, the refractive index does not vary with ice phase.

Graphical abstract: A new technique for determining the refractive index of ices at cryogenic temperatures

Supplementary files

Article information

Article type
Paper
Submitted
02 May 2020
Accepted
19 Oct 2020
First published
21 Oct 2020
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2020,22, 25353-25365

A new technique for determining the refractive index of ices at cryogenic temperatures

J. W. Stubbing, M. R. S. McCoustra and W. A. Brown, Phys. Chem. Chem. Phys., 2020, 22, 25353 DOI: 10.1039/D0CP02373F

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