Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases

Shahnewaz M. Emtiaz, Francis Toriello, Jiao He, Gianfranco Vidali

Research output: Contribution to journalArticle

Abstract

Infrared spectroscopy was employed to study thin films of solid methane at low temperatures. We report new measurements of temporal changes of infrared spectra of methane ice in the ν3 and ν4 bands due to nuclear spin conversion upon rapid cooling from 30 to 6.0-11.0 K. The relaxation rates of the nuclear spin were found to be a function of temperature. The activation energy associated with the relaxation has been determined over an extended temperature range. We also found a new metastable phase of methane ice upon deposition at T < 7 K. After the deposition at 6 K and annealed to a higher temperature, a phase transition from the metastable phase to a stable crystalline phase takes place. We found that the relaxation has different activation energies below and above 8.5 K. From a quantitative analysis of the ν3 and ν4 IR bands, we suggest that the metastable phase is a crystalline phase with a degree of orientational disorder between the two known stable solid phases.

Original languageEnglish (US)
Pages (from-to)552-559
Number of pages8
JournalJournal of Physical Chemistry A
Volume124
Issue number3
DOIs
StatePublished - Jan 23 2020

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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