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Infrared Spectra of Mass-Selected Br¯−(NH_3)_n and I¯−NH_3 Clusters

Wild, Duncan A. and Kuwata, Keith T. and Wong, Chi-Kin and Lobo, Julio D. and Deev, Andrei and Schindler, Thomas S. and Okumura, Mitchio and Bieske, Evan J. (2010) Infrared Spectra of Mass-Selected Br¯−(NH_3)_n and I¯−NH_3 Clusters. Journal of Physical Chemistry A, 114 (14). pp. 4762-4769. ISSN 1089-5639. http://resolver.caltech.edu/CaltechAUTHORS:20100520-112901491

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Abstract

Infrared vibrational predissociation spectra are recorded for Br¯−(NH_3)_n (n = 1−4) and I¯−NH_3 clusters in the N−H stretch region (3040−3460 cm^(−1)). To aid spectral assignments and clarify structures of the Br¯−(NH_3)_n clusters, ab initio calculations are performed at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels of theory. The Br¯−NH_3 and I¯−NH_3 dimers are predicted to have structures in which the NH_3 molecule is attached to the halide anion by a single hydrogen-bond. The dominant infrared band for Br¯−NH_3 at 3171 cm^(−1) corresponds to a hydrogen-bonded N−H stretch vibrational mode, whereas two weaker bands are assigned to a symmetric stretch vibration of the nonbonded N−H groups (3347 cm^(−1)) and to an ammonia-based bending overtone (3293 cm^(−1)) deriving infrared intensity through Fermi interaction with the H-bonded N−H stretch mode. The corresponding I¯−NH3 spectrum is dominated by the H-bonded N−H stretch band at 3217 cm^(−1), with three weaker bands at 3240, 3305, and 3360 cm^(−1) assigned to two bending overtone vibrations and the nonbonded N−H symmetric stretch vibration, respectively. Spectra of the Br¯−(NH_3)_n, n = 2−4, clusters are similar to the I¯−NH_3 spectrum, exhibiting evidence for strong Fermi interactions between the H-bonded N−H stretch vibrational mode and ammonia-based bending overtones. On the basis of the infrared spectra and ab initio calculations, the larger Br¯−(NH_3)_n clusters are deduced to have structures in which the NH_3 molecules are attached to the Br¯ by single H-bonds, but not necessarily to one other.


Item Type:Article
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http://dx.doi.org/10.1021/jp909237nDOIArticle
http://pubs.acs.org/doi/abs/10.1021/jp909237nPublisherArticle
ORCID:
AuthorORCID
Okumura, Mitchio0000-0001-6874-1137
Additional Information:© 2010 American Chemical Society. Received: September 25, 2009; revised manuscript received: December 14, 2009. Financial support is acknowledged from the Australian Research Council, the University of Melbourne, and the MPI für biophysikalische Chemie. D.A.W. acknowledges discussions with Dr. Thomas Lenzer and the provision of computer time at the MPI für biophysikalische Chemie, Göttingen, Germany. M.O. and K.T.K. acknowledge the support of the National Science Foundation Grant CHE-9700610 and a Graduate Fellowship.
Funders:
Funding AgencyGrant Number
Australian Research CouncilUNSPECIFIED
University of MelbourneUNSPECIFIED
MPI für biophysikalische ChemieUNSPECIFIED
NSFCHE-9700610
NSF Graduate FellowshipUNSPECIFIED
Record Number:CaltechAUTHORS:20100520-112901491
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100520-112901491
Official Citation:Infrared Spectra of Mass-Selected Br−−(NH3)n and I−−NH3 Clusters Duncan A. Wild, Keith T. Kuwata, Chi-Kin Wong, Julio D. Lobo, Andrei Deev, Thomas S. Schindler, Mitchio Okumura, Evan J. Bieske The Journal of Physical Chemistry A 2010 114 (14), 4762-4769
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18360
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:21 May 2010 20:31
Last Modified:14 Sep 2015 23:59

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