Multidimensional dynamics in the electron stimulated desorption of ammonia from Pt(111)

Journal Article · Sat Oct 01 04:00:00 EDT 1994 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.468385· OSTI ID:7071684

Burns, A R; Stechel, E B; Jennison, D R ^[1]; Li, Y S ^[2]

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1. Sandia National Laboratories, Albuquerque, New Mexico 87185-0344 (United States)
2. Biosym Technologies, San Diego, California 92121-3752 (United States)

We characterize the electron stimulated desorption of neutral ammonia (NH[sub 3] and ND[sub 3]) from Pt(111) with vibrational and rotational quantum resolution by using (2+1) resonance enhanced multiphoton ionization detection. Two significant isotope effects appear: (1) the desorption yield of NH[sub 3] is three times that of ND[sub 3] and (2) NH[sub 3] desorbs with considerably more spinning'' rotational energy than does ND[sub 3]. We find virtually identical translational energy distributions for each desorbate and roughly equal vibrational energy distributions. Vibrational excitation is found exclusively in the [nu][sub 2] symmetric deformation or umbrella'' mode, independent of isotope. These effects [ital cannot] be explained by desorption induced by vibrational energy transfer. Instead, desorption is the result of excitation of a 3[ital a][sub 1] electron principally on the N atom, which causes the pyramidal NH[sub 3] adsorbate to rapidly [ital invert]. [ital Ab] [ital initio] calculations of [ital two]-[ital dimensional] potential energy surfaces (intramolecular bond angle and surface bond length) reveal that near-inverted molecules deexcite to a repulsive hard wall of the adsorbate--substrate interaction and desorb. Spinning excitation derives from the rotational barrier of the inverted molecule. Both isotope effects are direct consequences of desorption via inversion. In general, multidimensional dynamics [ital must] be considered in the study of stimulated surface processes. Our calculations also indicate that excited-state forces at equilibrium molecule--surface distances are an order of magnitude less than those derived from a currently accepted image-potential model.

• OSTI ID: 7071684
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 101:7; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
665300* -- Interactions Between Beams & Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMMONIA
COLLISIONS
DESORPTION
DEUTERIUM COMPOUNDS
DYNAMICS
ELECTRON COLLISIONS
ELEMENTS
ENERGY
ENERGY LEVELS
EXCITED STATES
HYDRIDES
HYDROGEN COMPOUNDS
ISOTOPE EFFECTS
MANY-DIMENSIONAL CALCULATIONS
MASS SPECTROSCOPY
MECHANICS
METALS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PLATINUM
PLATINUM METALS
POTENTIAL ENERGY
RESOLUTION
RESONANCE IONIZATION MASS SPECTROSCOPY
ROTATIONAL STATES
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENTS
VIBRATIONAL STATES
YIELDS