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Title: Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations

Abstract

Infrared spectra of the NH stretching vibrations of (NH 3) n clusters (n=2-4) have been obtained using the helium droplet isolation technique and first principles electronic structure anharmonic calculations. The measured spectra exhibit well-resolved bands, which have been assigned to the v 1, v 3, and 2v 4 modes of the ammonia fragments in the clusters. The formation of a hydrogen bond in ammonia dimers leads to an increase of the infrared intensity by about a factor of four. In the larger clusters the infrared intensity per hydrogen bond is close to the one for dimers and approaches the value in the NH 3 crystal. The intensity of the 2v 4 overtone band in the trimer and tetramer increases by a factor of 10 relative to that in the monomer and dimer, and is comparable to the intensity of the v 1 and v 3 fundamental bands in larger clusters. This indicates the onset of the strong anharmonic coupling of the 2v 4 and v 1 modes in larger clusters. The experimental assignments are compared to the ones obtained from first principles electronic structure anharmonic calculations for the dimer and trimer clusters. The anharmonic calculations were performed at themore » Møller-Plesset (MP2) level of electronic structure theory and were based on a second-order perturbative evaluation of rovibrational parameters and their effects on the vibrational spectra and average structures. In general there is excellent (<20 cm -1) agreement between the experimentally measured band origins for the N-H stretching frequencies and the calculated anharmonic vibrational frequencies. However, the calculations were found to overestimate the infrared intensities in clusters by about a factor of four. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
915703
Report Number(s):
PNNL-SA-53939
Journal ID: ISSN 1089-5639; JPCAFH; KC0301020; TRN: US200816%%165
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 111; Journal Issue: 31; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; AMMONIA; DIMERS; ELECTRONIC STRUCTURE; EVALUATION; HELIUM; HYDROGEN; INFRARED SPECTRA; MONOMERS; SPECTRA; SPECTROSCOPY

Citation Formats

Slipchenko, Mikhail N, Sartakov, Boris G, Vilesov, Andrey F, and Xantheas, Sotiris S. Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations. United States: N. p., 2007. Web. doi:10.1021/jp071279+.
Slipchenko, Mikhail N, Sartakov, Boris G, Vilesov, Andrey F, & Xantheas, Sotiris S. Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations. United States. https://doi.org/10.1021/jp071279+
Slipchenko, Mikhail N, Sartakov, Boris G, Vilesov, Andrey F, and Xantheas, Sotiris S. Thu . "Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations". United States. https://doi.org/10.1021/jp071279+.
@article{osti_915703,
title = {Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations},
author = {Slipchenko, Mikhail N and Sartakov, Boris G and Vilesov, Andrey F and Xantheas, Sotiris S},
abstractNote = {Infrared spectra of the NH stretching vibrations of (NH3)n clusters (n=2-4) have been obtained using the helium droplet isolation technique and first principles electronic structure anharmonic calculations. The measured spectra exhibit well-resolved bands, which have been assigned to the v1, v3, and 2v4 modes of the ammonia fragments in the clusters. The formation of a hydrogen bond in ammonia dimers leads to an increase of the infrared intensity by about a factor of four. In the larger clusters the infrared intensity per hydrogen bond is close to the one for dimers and approaches the value in the NH3 crystal. The intensity of the 2v4 overtone band in the trimer and tetramer increases by a factor of 10 relative to that in the monomer and dimer, and is comparable to the intensity of the v1 and v3 fundamental bands in larger clusters. This indicates the onset of the strong anharmonic coupling of the 2v4 and v1 modes in larger clusters. The experimental assignments are compared to the ones obtained from first principles electronic structure anharmonic calculations for the dimer and trimer clusters. The anharmonic calculations were performed at the Møller-Plesset (MP2) level of electronic structure theory and were based on a second-order perturbative evaluation of rovibrational parameters and their effects on the vibrational spectra and average structures. In general there is excellent (<20 cm-1) agreement between the experimentally measured band origins for the N-H stretching frequencies and the calculated anharmonic vibrational frequencies. However, the calculations were found to overestimate the infrared intensities in clusters by about a factor of four. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.},
doi = {10.1021/jp071279+},
url = {https://www.osti.gov/biblio/915703}, journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
issn = {1089-5639},
number = 31,
volume = 111,
place = {United States},
year = {2007},
month = {8}
}