Effect of Nitrogen Adsorption on the Mid-Infrared Spectrum of Water Clusters

Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, D-38106 Braunschweig, Germany.
The Journal of Physical Chemistry A (Impact Factor: 2.69). 06/2011; 115(23):6218-25. DOI: 10.1021/jp111481q
Source: PubMed


Experimental Fourier-transform infrared spectra and DFT calculated infrared spectra are compared to investigate the effect of adsorbed nitrogen on the OH-stretch band complex of water clusters. Using a collisional cooling experiment, pure as well as partially and completely N(2)-covered water clusters consisting of 20-200 water molecules have been generated in thermal equilibrium in the aerosol phase within the temperature range of 5-80 K. Computational IR-spectra simulations have been performed for discrete pure and N(2)-covered water clusters including 10, 15, 20, and 30 water molecules. The adsorbed N(2) molecules especially affect the three-coordinated water molecules at the cluster surface which could be observed as a blue shift of the companion O-H band at 2900 cm(-1) and a red shift of the dangling O-H band at 3700 cm(-1) by about 20 cm(-1) in both cases. The most striking effect of the N(2) adsorbate is an intensity increase of the dangling O-H band by a factor of 3-5. Furthermore, the onset temperature of nitrogen adsorption at the water cluster surface was experimentally found to be roughly 30 K for cluster sizes of about 100 water molecules. Experimental and computational results are in good agreement. The presented results are based on and support the work of V. Buch, J. P. Devlin, and co-workers (e.g., J. Phys. Chem. B, 1997; J. Phys. Chem. A, 2003; Int. Rev. Phys. Chem., 2004).

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    • "ering our experimental results and the literature, the band at 3725 cm −1 is positively attributed to a water monomer interacting with the surface via its two electronic doublets; its large intensity compared to the other dH bands is explained by the magnifying effect of nitrogen, as extensively investigated by Hujo et al.[24]. We suggest that nitrogen molecules, present as a lowlevel pollutant in the chamber, serendipitously complex the water molecule, as illustrated in Figure 4, stabilising the molecule, preventing any further adsorption, and magnifying the OH stretching bands. "
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