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We have previously analyzed a band of the NO$_3$ radical observed at 1492\wn and have established that the band was of $E$ type, thus being assigned to the degenerate N-O stretching, \nub {3} }. We have explained several anomalies noticed in the band in terms of a vibronic interaction model }. Stanton } recently proposed an alternative assignment \nub {1} + \nub {4} for this band, primarily based on an $ab ~initio$ calculated potential. In order to establish the vibrational assignment of the band, we applied the vibronic interaction modelc to the $^{14}$NO$_3$-$^{15}$NO$_3$ isotope shift and calculated it to be 16 \wn in reasonable agreement with the observed value of 20 \wn } when the band is \nub {3}, whereas we obtained a very small value (about 1 \wn or less) for Stanton's assignment, at variance with the observed data. We have also scanned the region from 700 up to 1400 \wn to detect the \nub {3} band predicted by Stanton at 994 \wn }, by using a Fourier transform spectrometer. Although some part of this region was covered by strong absorption of the precursor HNO$_3$, we confirmed that there were no bands observed between 925 and 1277 \wn that were more than 1/10 as intense as the 1492 \wn band.


T. Ishiwata et al. , J. Chem. Phys. 82, 2196 (1985), K. Kawaguchi et al. , J. Chem. Phys. 93, 951 (1990).E. Hirota et al. , J. Chem. Phys. 95, 771 (1991).F. Stanton, J. Chem. Phys. 126, 134309 (2007).T. Ishiwata et al. , J. Chem. Phys. 82, 2196 (1985).F. Stanton, J. Chem. Phys. 126, 134309 (2007).
Author Institution: The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan; Department of Chemistry, Okayama University, Tsushima-naka 3-1-1; Okayama 700-8530, Japan; Department of Information Machines and Interfaces, Faculty of; Information Sciences, Hiroshima City University, Ozukahigashi, Asaminami; Hiroshima 731-3194, Japan; Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro, Tokyo 152-8550, Japan