Velocity-aligned Doppler spectroscopy

Journal Article · Wed Mar 01 04:00:00 EST 1989 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.455967· OSTI ID:6548534

Xu, Z; Koplitz, B; Wittig, C

The technique of velocity-aligned Doppler spectrosocopy (VADS) is presented and discussed. For photolysis/probe experiments with pulsed initiation, VADS can yield Doppler profiles for nascent photofragments that allow detailed center-of-mass (c.m.) kinetic energy distributions to be extracted. When compared with traditional forms of Doppler spectroscopy, the improvement in kinetic energy resolution is dramatic. Changes in the measured profiles are a consequence of spatial discrimination (i.e., focused and overlapping photolysis and probe beams) and delayed observation. These factors result in the selective detection of species whose velocities are aligned with the wave vector of the probe radiation k/sub pr/, thus revealing the speed distribution along k/sub pr/ rather than the distribution of nascent velocity components projected upon this direction. Mathematical details of the procedure used to model VADS are given, and experimental illustrations for HI, H/sub 2/S, and NH/sub 3/ photodissociation are presented. In these examples, pulsed photodissociation produces H atoms that are detected by sequential two-photon, two-frequency ionization via Lyman-..cap alpha.. with a pulsed laser (121.6+364.7 nm), and measuring the Lyman-..cap alpha.. Doppler profile as a function of probe delay reveals both internal and c.m. kinetic energy distributions for the photofragments. Strengths and weaknesses of VADS as a tool for investigating photofragmentation phenomena are also discussed.

• Research Organization: Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482
• OSTI ID: 6548534
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 90:5; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
440300 -- Miscellaneous Instruments-- (-1989)
47 OTHER INSTRUMENTATION
AMMONIA
CHALCOGENIDES
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
DECOMPOSITION
DISSOCIATION
DISTRIBUTION
DOPPLER COEFFICIENT
ELEMENTS
ENERGY
FRAGMENTATION
HALOGEN COMPOUNDS
HYDRIDES
HYDRIODIC ACID
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
INORGANIC ACIDS
IODINE COMPOUNDS
KINETIC ENERGY
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
REACTIVITY COEFFICIENTS
RESOLUTION
SPECTROSCOPY
SULFIDES
SULFUR COMPOUNDS
VELOCITY
YIELDS