Infrared spectra of mass-selected clusters NOf(H20), for n = 1 to 5 were recorded from 2700 to 3800 cm-' by vibrational predissociation spectroscopy. Vibrational frequencies and intensities were also calculated for n= 1 and 2 at the second-order MQller-Plesset (MP2) level, to aid in the interpretation of the spectra, and at the singles and doubles coupled cluster (CCSD) level energies of it = 1 isomers were computed at the MP2 geometries. The smaller clusters (n = 1 to 3) were complexes of HZ0 ligands bound to a nitrosonium ion NO+ core. They possessed perturbed HZ0 stretch bands and dissociated by loss of H,O. The Ha0 antisymmetric stretch was absent in y1= 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-' and two new minor photodissociation channels, loss of HONO and loss of two HZ0 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 H30'(H20)s(HONO), i.e., an adduct of the reaction products.
Infrared spectra of clusters of protonated nitric acid and water exhibit a marked change with cluster size, indicating that an intracluster reaction occurs with sufficient solvation. In small clusters, H 2 0 binds to a nitronium ion core, but at a critical cluster size the NO{ reacts. A lower bound of 174 kcal!mol is found for the proton affinity of HN0 3 •
Silanium ions are an important class of hypervalent molecules, and the determination of their structure will yield insights into the nature of nonclassical bonding and provide a contrast to the bonding in carbonium ions. We report the infrared spectrum of the mass-selected silicon hydride cluster ion 28SiH7, detected by vibrational predissociation spectroscopy. Silanium ions were foimed in a pulsed high pressure glow discharge and cooled by the subsequent supersonic expansion. Photodissociation spectra were obtained using a tandem time-of-flight mass spectrometer: SiH7 ions were mass-selected and excited by a tunable infrared laser. The resulting photofragments were detected using a reflectron as a mass analyzer. We observed a vibrational band at 3865 cm1, which was the only one observed from 3500 cm1 to 4200 cm1. This result suggests that the molecule might form a symmetric complex with the structure H2 SiH3H2, in contrast to the species CH7, which has the structure CH5H2.
Predissociation spectra in the 2.6−3.3 μm region were observed
for protonated chlorine nitrate and protonated
nitric acid as well as some of their isotopomers
(HXNO3
+, X = H, D,
35Cl, 37Cl). Two protonated
isomers
of both ClONO2 and HNO3 were identified from
the vibrational spectra. The lowest energy isomer was
the
ion−molecule complex NO2
+(HOX) formed
by protonation of the XO group. The second isomer was
the
metastable species (HO)(XO)NO+ formed by
protonation of a terminal oxygen; this isomer was
generated
only under hotter ionizing conditions. The vibrational band
centers of these isomers agreed well with ab
initio predictions. Vibrational excitation of the
HXNO3
+ species studied here led solely to
NO2
+ + HOX
products. Predissociation of the covalently bound metastable
isomers (HO)(XO)NO+ to these products
required
an IR-induced rearrangement involving simultaneous 1,3 hydrogen shift
and charge transfer. The results
presented here were consistent with predictions of ab initio
calculations and previous mass spectrometric and
kinetic studies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.