Dresden 2011 – scientific programme
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MO: Fachverband Molekülphysik
MO 10: Cluster
MO 10.5: Talk
Tuesday, March 15, 2011, 11:30–11:45, MER 02
IR Spectroscopy of Microhydrated Nitrate Ions: Influence of Solvent and Temperature on Structure — •Nadja Heine1, Torsten Wende1, Ling Jiang1, Risshu Bergmann1, Kenneth D. Jordan2, Gerard Meijer1, and Knut R. Asmis1 — 1Fritz-Haber-Institut der MPG, Berlin — 2University of Pittsburgh, USA
Nitrate ions, NO3−, play an important role in atmospheric chemistry, nuclear waste treatment and biochemical processes. For instance, NO3− is one of the most abundant ions in the troposphere and can be formed by rapid acid dissolution of nitric acid in aerosol particles. For a molecular-level understanding of such processes the characterization of their hydration behavior is crucial. Here, we exploit infrared photodissociation (IRPD) spectroscopy for obtaining structural information on the nitrate-solvent complexes using a time-of-flight tandem mass spectrometer combined with an ion trap. We present IRPD spectra of NO3−·(H2O)1−4 as well as selected deuterated analogs, measured in the OH-/OD-stretching region (2400 - 3800 cm−1) and at ion trap temperatures between 10 to 300 K. The present measurements complement our previous IRPD study of hydrated nitrate ions in the fingerprint region. The IRPD spectra of NO3−·(H2O) and NO3−·(D2O) in the OH-stretch region confirm a bidentate binding motif at low temperatures. At higher temperatures an additional isomer with just a single hydrogen bond is observed. The complex sequence in the OH-stretching region suggest a strong anharmonic coupling between the OH-stretch modes and low-frequency modes, which is modeled using vibrational CI calculations on a 15-dimensional potential energy surface.