Molecular desorption from ionic molecular crystals following resonant UV excitation

Conference · Tue Oct 01 04:00:00 EDT 1996

OSTI ID:370168

Hess, W P; German, K A.H.; Bradley, R A ^[1]

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1. Pacific Northwest National Lab., Richland, WA (United States)

We have studied desorption from molecular ionic crystals following pulsed UV excitation of localized valence states of the molecular anion. The excitation laser flux is maintained at low levels (< 2 MW/cm{sup 2}) to produce desorption yields of no more than 1% of a monolayer per pulse. The low yields provide desorbed product species free of secondary interactions following fragment ejection from the crystal surface. At low fluence, the photodesorption yields from cleaved sodium nitrate and calcite single crystals are found to be linear with desorption laser power. In both cases, product distributions are far removed from the surface stoichiometry, with NO and CO being the dominant fragments from NaNO{sub 3} and CaCO{sub 3} respectively. In the case of NaNO{sub 3}, the desorption yield for NO is enhanced by a factor of at least 1000 for resonant excitation over nonresonant excitation. The rotational state populations and translational energy distributions of the NO are well characterized by thermal distributions. The observed vibrational levels, however, are highly excited. State distribution studies of CO ejected from CaCO{sub 3} indicate that the CO vibrational levels are excited, but not as dramatically as the NO molecules. A local excitation mechanism for desorption is proposed.

• OSTI ID: 370168
• Report Number(s): CONF-960376--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ATMOSPHERIC CHEMISTRY
CALCITE
CARBON MONOXIDE
CRYSTALS
DESORPTION
EXCITATION
IONIC CRYSTALS
MOLECULAR CRYSTALS
NITRIC OXIDE
PHOTOCHEMICAL REACTIONS
SODIUM NITRATES
STOICHIOMETRY
ULTRAVIOLET RADIATION
VALENCE