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 Brˉ−(NH_3)_n and Iˉ−NH_3 Clusters. Journal of Physical Chemistry A, 114 (14). pp. 4762-4769. ISSN 1089-5639 http://resolver.caltech.edu/CaltechAUTHORS:20100525-113700076
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Infrared vibrational predissociation spectra are recorded for Brˉ−(NH_3)_n (n = 1−4) and Iˉ−NH_3 clusters in the N−H stretch region (3040−3460 cm^(−1)). To aid spectral assignments and clarify structures of the Brˉ−(NH_3)_n clusters, ab initio calculations are performed at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels of theory. The Brˉ−NH_3 and Iˉ−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 Brˉ−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 Iˉ−NH_3 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 Brˉ−(NH_3)_n, n = 2−4, clusters are similar to the Iˉ−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 Brˉ−(NH_3)_n clusters are deduced to have structures in which the NH_3 molecules are attached to the Brˉ by single H-bonds, but not necessarily to one other.
|Additional Information:||© 2010 American Chemical Society. Received: September 25, 2009; Revised Manuscript Received: December 14, 2009. Publication Date (Web): January 22, 2010. Financial support is acknowledged from the Australian Research Council, the University of Melbourne, and the MPI fu¨r biophysikalische Chemie. D.A.W. acknowledges discussions with Dr. Thomas Lenzer and the provision of computer time at the MPI fu¨r biophysikalische Chemie, Go¨ttingen, Germany. M.O. and K.T.K. acknowledge the support of the National Science Foundation Grant CHE-9700610 and a Graduate Fellowship.|
|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|
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|Deposited By:||Jason Perez|
|Deposited On:||02 Jun 2010 16:17|
|Last Modified:||26 Dec 2012 12:04|
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