TY - JOUR
T1 - Vacuum ultraviolet surface photochemistry of water adsorbed on graphite
AU - Baggott, SR
AU - Kolasinski, KW
AU - Perdigao, Luis
AU - Riedel, Damien
AU - Guo, Quanmin
AU - Palmer, Richard
PY - 2002/1/1
Y1 - 2002/1/1
N2 - We report a study of the vacuum ultraviolet (VUV) surface photochemistry of H2O (D2O) films on a graphite substrate at 80 K. Experiments utilized a He discharge lamp to generate VUV photons. For 21 eV excitation, H+ (D+) is the only ionic fragment observed in desorption. When 41-eV photons are used, H+ (D+) is again observed: however, photochemically produced H3O+ (D3O+) is also detected. The ratio of D+ to D3O+ depends upon the water coverage. Furthermore, the D3O+ signal is larger than D+, whereas the H3O+ signal is smaller than H+ for irradiation of adsorbed D2O and H2O, respectively. At low coverages where the average coordination of water is also lower, D3O+ production is enhanced compared with higher coverages. The formation of D3O+ is attributed to the reaction of the photodissociation product D+ with adsorbed D2O. We suggest that the opening of the D3O+ product channel at 41 eV and its preponderance over D+ is related to the higher kinetic energy of, and consequently greater momentum transfer by, the D+ ions created through D2O photodissociation at this photon energy. We also suggest that there is a propensity for a hydrogen bonded O-D to break preferentially over a free O-D bond after photoexcitation. (C) 2002 American Institute of Physics.
AB - We report a study of the vacuum ultraviolet (VUV) surface photochemistry of H2O (D2O) films on a graphite substrate at 80 K. Experiments utilized a He discharge lamp to generate VUV photons. For 21 eV excitation, H+ (D+) is the only ionic fragment observed in desorption. When 41-eV photons are used, H+ (D+) is again observed: however, photochemically produced H3O+ (D3O+) is also detected. The ratio of D+ to D3O+ depends upon the water coverage. Furthermore, the D3O+ signal is larger than D+, whereas the H3O+ signal is smaller than H+ for irradiation of adsorbed D2O and H2O, respectively. At low coverages where the average coordination of water is also lower, D3O+ production is enhanced compared with higher coverages. The formation of D3O+ is attributed to the reaction of the photodissociation product D+ with adsorbed D2O. We suggest that the opening of the D3O+ product channel at 41 eV and its preponderance over D+ is related to the higher kinetic energy of, and consequently greater momentum transfer by, the D+ ions created through D2O photodissociation at this photon energy. We also suggest that there is a propensity for a hydrogen bonded O-D to break preferentially over a free O-D bond after photoexcitation. (C) 2002 American Institute of Physics.
UR - http://www.scopus.com/inward/record.url?scp=0037044536&partnerID=8YFLogxK
U2 - 10.1063/1.1506143
DO - 10.1063/1.1506143
M3 - Article
SN - 0021-9606
VL - 117
SP - 6667
EP - 6672
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 14
ER -