Mechanisms of H2O Desorption from Amorphous Solid Water by 157-nm Irradiation: An Experimental and Theoretical Study

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dc.contributor.author DeSimone, Alice J.
dc.contributor.author Crowell, Vernon D.
dc.contributor.author Sherrill, C. David
dc.contributor.author Orlando, Thomas M.
dc.date.accessioned 2018-10-24T14:07:17Z
dc.date.available 2018-10-24T14:07:17Z
dc.date.issued 2013-10-23
dc.identifier.citation DeSimone, A., Crowell, V., Sherrill, C., Orlando, T. (2013): Mechanisms of H2O Desorption from Amorphous Solid Water by 157-nm Irradiation: An Experimental and Theoretical Study. The Journal of Chemical Physics, 139. en_US
dc.identifier.uri http://ir.ua.edu/handle/123456789/4095
dc.description.abstract The photodesorption of water molecules from amorphous solid water (ASW) by 157-nm irradiation has been examined using resonance-enhanced multiphoton ionization. The rotational temperature has been determined, by comparison with simulations, to be 425 ± 75 K. The time-of-flight spectrum of H2O (v = 0) has been fit with a Maxwell-Boltzmann distribution with a translational temperature of 700 ± 200 K (0.12 ± 0.03 eV). H+ and OH+ fragment ions have been detected with non-resonant multiphoton ionization, indicating vibrationally excited parent water molecules with translational energies of 0.24 ± 0.08 eV. The cross section for water removal from ASW by 7.9-eV photons near 100 K is (6.9 ± 1.8) × 10−20 cm2 for >10 L H2O exposure. Electronic structure computations have also probed the excited states of water and the mechanisms of desorption. Calculated electron attachment and detachment densities show that exciton delocalization leads to a dipole reversal state in the first singlet excited state of a model system of hexagonal water ice. Ab Initio Molecular Dynamics simulations show possible desorption of a photo-excited water molecule from this cluster, though the non-hydrogen bonded OH bond is stretched significantly before desorption. Potential energy curves of this OH stretch in the electronic excited state show a barrier to dissociation, lending credence to the dipole reversal mechanism. en_US
dc.subject Photoionization en_US
dc.subject Amorphous solids en_US
dc.subject Resonance-enhanced multiphoton ionization en_US
dc.subject Delocalization en_US
dc.subject Maxwell-Boltzmann distribution en_US
dc.subject Surface and interface chemistry en_US
dc.subject Molecular dynamics en_US
dc.subject Excitons en_US
dc.subject Photodesorption en_US
dc.subject Potential energy surfaces en_US
dc.title Mechanisms of H2O Desorption from Amorphous Solid Water by 157-nm Irradiation: An Experimental and Theoretical Study en_US
dc.type text en_US


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