Water photodissociation in free ice nanoparticles at 243 nm and 193 nm

J. Heyrovský Institute of Physical Chemistry, v.v.i. Academy of Sciences of the Czech Republic, Prague 8, Czech Republic.
Physical Chemistry Chemical Physics (Impact Factor: 4.49). 09/2008; 10(32):4835-42. DOI: 10.1039/b806865h
Source: PubMed


The photolysis of (H(2)O)(n) nanoparticles of various mean sizes between 85 and 670 has been studied in a molecular beam experiment. At the dissociation wavelength 243 nm (5.10 eV), a two-photon absorption leads to H-atom production. The measured kinetic energy distributions of H-fragments exhibit a peak of slow fragments below 0.4 eV with maximum at approximately 0.05 eV, and a tail of faster fragments extending to 1.5 eV. The dependence on the cluster size suggests that the former fragments originate from the photodissociation of an H(2)O molecule in the cluster interior leading to the H-fragment caging and eventually generation of a hydronium H(3)O molecule. The photolysis of surface molecules yields the faster fragments. At 193 nm (6.42 eV) a single photon process leads to a small signal from molecules directly photolyzed on the cluster surface. The two photon processes at this wavelength may lead to cluster ionization competing with its photodissociation, as suggested by the lack of H-fragment signal increase. The experimental findings are complemented by theoretical calculations.

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    • "The details of ice nanoparticles generation in supersonic expansions has been recently investigated by Kim et al. (2004), Manka et al. (2012), and Li et al. (2013). The individual particles can be investigated under controlled conditions in vacuum by various means: e.g., ionization (electron, photon) and mass spectrometry (MacTaylor and Castleman, 2000; Lengyel et al., 2012b); infrared (IR) spectroscopy (Yacovitch et al., 2011, 2012; Preston et al., 2012; Fujii and Mizuse, 2013) or ultraviolet (UV) photodissociation experiments (Kreher et al., 1999; Li and Huber, 2001; Poterya et al., 2007, 2008a, 2011; Ončák et al., 2008, 2011); particle (electron , photon, neutron) scattering (Heath et al., 2003; Kim et al., 2004; Manka et al., 2012); special methods such as sodium doping and subsequent spectroscopies (Bobbert et al., 2002; Yoder et al., 2011; Pradzynski et al., 2012). Such experiments provide unprecedented molecular-level insight into the small particle generation , their (photo)chemistry and (photo)physics and detailed dynamics of the processes on/in these particles. "
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