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Vibrational Sum Frequency Generation (VSFG) Spectroscopy Measurement of the Rotational Barrier of Methyl Groups on Methyl-Terminated Silicon(111) Surfaces

Bhattacharyya, Dhritiman and Montenegro, Angelo and Plymale, Noah T. and Dutta, Chayan and Lewis, Nathan S. and Benderskii, Alexander V. (2019) Vibrational Sum Frequency Generation (VSFG) Spectroscopy Measurement of the Rotational Barrier of Methyl Groups on Methyl-Terminated Silicon(111) Surfaces. Journal of Physical Chemistry Letters, 10 (18). pp. 5434-5439. ISSN 1948-7185. doi:10.1021/acs.jpclett.9b01487. https://resolver.caltech.edu/CaltechAUTHORS:20190826-085041693

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Abstract

The methyl-terminated Si(111) surface possesses a 3-fold in-plane symmetry, with the methyl groups oriented perpendicular to the substrate. The propeller-like rotation of the methyl groups is hindered at room temperature and proceeds via 120° jumps between three isoenergetic minima in registry with the crystalline Si substrate. We have used line-shape analysis of polarization-selected vibrational sum frequency generation spectroscopy to determine the rotational relaxation rate of the surface methyl groups and have measured the temperature dependence of the relaxation rate between 20 and 120 °C. By fitting the measured rate to an Arrhenius dependence, we extracted an activation energy (the rotational barrier) of 830 ± 360 cm^(–1) and an attempt frequency of (2.9 ± 4.2) × 10^(13) s^(–1) for the methyl rotation process. Comparison with the harmonic frequency of a methyl group in a 3-fold cosine potential suggests that the hindered rotation occurs via uncorrelated jumps of single methyl groups rather than concerted gear-like rotation.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/acs.jpclett.9b01487DOIArticle
ORCID:
AuthorORCID
Bhattacharyya, Dhritiman0000-0001-6761-8655
Plymale, Noah T.0000-0003-2564-8009
Dutta, Chayan0000-0003-4839-2245
Lewis, Nathan S.0000-0001-5245-0538
Benderskii, Alexander V.0000-0001-7031-2630
Additional Information:© 2019 American Chemical Society. Received: May 23, 2019; Accepted: August 23, 2019; Published: August 23, 2019. This research was supported by AFOSR Grant No. FA9550-15-1-0184. N.T.P. and N.S.L. acknowledge support from the National Science Foundation Grant No. CHE-1808599. D.B. acknowledges support from the Burg Teaching Fellowship from Anton Burg Foundation. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
Air Force Office of Scientific Research (AFOSR)FA9550-15-1-0184
NSFCHE-1808599
Anton Burg FoundationUNSPECIFIED
Issue or Number:18
DOI:10.1021/acs.jpclett.9b01487
Record Number:CaltechAUTHORS:20190826-085041693
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190826-085041693
Official Citation:Vibrational Sum Frequency Generation Spectroscopy Measurement of the Rotational Barrier of Methyl Groups on Methyl-Terminated Silicon(111) Surfaces. Dhritiman Bhattacharyya, Angelo Montenegro, Noah T. Plymale, Chayan Dutta, Nathan S. Lewis, and Alexander V. Benderskii. The Journal of Physical Chemistry Letters 2019 10 (18), 5434-5439. DOI: 10.1021/acs.jpclett.9b01487
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98204
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:26 Aug 2019 16:03
Last Modified:16 Nov 2021 17:37

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