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Published May 15, 1994 | Published
Journal Article Open

Vibrational spectroscopy of NO^+(H_2O)_n: Evidence for the intracluster reaction NO^+(H_2O)_n→H_3O^+(H_2O)_(n-2)(HONO) at n≥4


Infrared spectra of mass‐selected clusters NO^+(H_2O)_n for n=1 to 5 were recorded from 2700 to 3800 cm^(−1) by vibrational predissociation spectroscopy. Vibrational frequencies and intensities were also calculated for n=1 and 2 at the second‐order Møller–Plesset (MP2) level, to aid in the interpretation of the spectra, and at the singles and doubles coupled cluster (CCSD) level energies of n=1 isomers were computed at the MP2 geometries. The smaller clusters (n=1 to 3) were complexes of H_2O ligands bound to a nitrosonium ion NO^+ core. They possessed perturbed H_2O stretch bands and dissociated by loss of H_2O. The H_2O antisymmetric stretch was absent in n=1 and gradually increased in intensity with n. In the n=4 clusters, we found evidence for the beginning of a second solvation shell as well as the onset of an intracluster reaction that formed HONO. These clusters exhibited additional weak, broad bands between 3200 and 3400 cm^(−1) and two new minor photodissociation channels, loss of HONO and loss of two H_2O molecules. The reaction appeared to go to completion within the n=5 clusters. The primary dissociation channel was loss of HONO, and seven vibrational bands were observed. From an analysis of the spectrum, we concluded that the n=5 cluster rearranged to form H_3O^+(H_2O)_3(HONO), i.e., an adduct of the reaction products.

Additional Information

© 1994 American Institute of Physics. Received 3 January 1994; accepted 7 February 1994. We acknowledge support of an NSF Presidential Young Investigator Award No. CHEM-8957423, E. I. DuPont de-Nemours and Company, the Irvine Foundation, the Chevron Fund, an AT&T Special Purpose Grant, an NSF predoctoral fellowship for K. T. K,, and the JPL Supercomputer Project for the computational studies. We are grateful to Mary Frances Jagod for her heroic efforts in reprogramming the asymmetric rotor spectrum prediction program ASMWIR, and to the Materials and Molecular Simulations Center of the Beckman Institute for the graphics facilities used in generating Fig. 6.

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August 20, 2023
August 20, 2023