Cassidy, A, James, RL orcid.org/0000-0002-5587-6590, Dawes, A et al. (1 more author) (2020) Crystallites and Electric Fields in Solid Ammonia. ChemistryOpen, 9 (10). pp. 983-990. ISSN 2191-1363
Abstract
Absorption spectra of vacuum-deposited films of ammonia have been obtained in the range 115 nm to 310 nm for a set of 15 deposition temperatures, Td, between 20 K and 80 K. Results focus upon the region 115 nm to 130 nm in overlapping D, E, F and G←X Rydberg transitions involving Wannier-Mott excitons. We identify two phases of ammonia, showing the solid to be polymorphic. Peak absorption wavelengths in the region of interest are found to shift to the red by 299 cm−1, for Td between 20 K to 50 K, and 1380 cm−1 for Td between 55 K to 80 K. Shifts provide evidence for the presence of spontaneously generated electric fields in these films, of values in excess of 108 V m−1 for Td of 20 K to 50 K to a few times 107 V m−1 for 55 K to 80 K. Results enable us to place a lower limit of 1.58 nm on the size of crystallites in the low temperature regime. This dimension represents 16 unit cells or 64 species, giving a more quantitative description than the nebulous term amorphous, as applied to solid ammonia. We also determine that crystallites formed in the high temperature regime contain, within ±20 %, 1688, 756 and 236 molecules of ammonia, respectively at Td of 65 K, 60 K and 55 K.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License,which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
Keywords: | Wannier-Mott exciton; spectroscopy; ammonia; molecular ices; polarised solids |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemistry (Leeds) > Physical Chemistry (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 08 Mar 2023 10:54 |
Last Modified: | 08 Mar 2023 10:54 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/open.202000118 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:197096 |
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