Anharmonic coupling of vibrational modes in atom--polyatomic collisions: A time-correlation function treatment

Journal Article · Sat Oct 15 04:00:00 EDT 1983 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.446244· OSTI ID:5541361

Vilallonga, E; Micha, D A

The role of molecular anharmonicity in hyperthermal collisions of atoms with polyatomic targets is investigated using a time-correlation function approach. By means of a cumulant expansion, the vibrational correlation is expressed in terms of displacement--displacement correlation functions, which are evaluated from the corresponding double-time Green functions; these in turn are obtained from their hierarchy of equations of motion. For a general intramolecular potential that contains anharmonic couplings between all the vibrational modes, the hierarchy is closed by means of a decoupling procedure that conserves the first few frequency moments of the spectral function. Consequently, the correlation functions can be evaluated analytically without need of internal state expansions, and they include the effects of anharmonic forces to infinite order. As examples, the targets CO/sub 2/, N/sub 2/O, and OCS are studied in detail, using spectroscopically derived vibrational potentials that contain quadratic through quartic terms; the roles of intra- and intermode anharmonic couplings are carefully considered. Differential cross sections for vibrational excitation calculated with the anharmonic potential are compared with those obtained from the harmonic model, for the systems Li/sup +//CO/sub 2/ and Li/sup +//N/sub 2/O at the collision energy E = 4.72 eV. Results indicate that anharmonic forces make a small (15% to 25%) contribution to the vibrational energy transferred to these targets in hyperthermal collisions.

• Research Organization: Departments of Physics and Chemistry, University of Florida, Gainesville, Florida 32611
• OSTI ID: 5541361
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 79:8; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CARBON OXYSULFIDE
CHALCOGENIDES
CHARGED PARTICLES
COLLISIONS
CORRELATION FUNCTIONS
CORRELATIONS
COUPLING
CROSS SECTIONS
DIFFERENTIAL CROSS SECTIONS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXCITED STATES
FUNCTIONS
ION COLLISIONS
ION-MOLECULE COLLISIONS
IONS
LITHIUM IONS
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NITROGEN OXIDES
NITROUS OXIDE
OSCILLATION MODES
OXIDES
OXYGEN COMPOUNDS
SULFUR COMPOUNDS
VIBRATIONAL STATES