Dynamics of infrared photodissociation of van der Waals molecules containing ethylene: an experimental study

Journal Article · Wed Jun 15 00:00:00 EDT 1983 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.444759· OSTI ID:6301653

Bomse, D S; Cross, J B; Valentini, J J

Infrared (approx.950 cm/sup -1/) predissociation of ethylene clusters has been studied using a crossed laser beam--molecular beam apparatus equipped with a moveable detector. van der Waals molecules undergo dissociation following absorption of a single infrared photon. Angular distributions, obtained for product molecules (C/sub 2/H/sub 4/)/sub n/, n = 1--3, all show nearly exponentially decreasing product flux with increasing scattering angle. A product flux contour map has been generated for the photolysis reaction (C/sub 2/H/sub 4/)/sub 2/ ..-->.. C/sub 2/H/sub 4/+C/sub 2/H/sub 4/. Two isotropic center-of-mass distribution functions yield excellent agreement with experimental results. One is a function of reaction kinetic energy E, with P(E) = exp(-E/80 cm/sup -1/); the other is a function of product velocity (momentum) u, with U(u) = u exp(-u/9 x 10/sup 3/ cm/s). The latter distribution is characteristic of a dissociation pathway with a barrier in the exit channel. Such a barrier could result from centrigufal effects. It is argued that isotropic product scattering can be consistent with a direct dissociation reaction occurring on the subpicosecond time scale. It is not possible to determine, unambiguously, if dissociation is direct or if the reaction proceeds through a long-lived intermediate. Experimental results indicate that only a small fraction of the energy available to products appears as translation, with the remainder appearing as rotational excitation of C/sub 2/H/sub 4/. Results are compared with other experimental studies on infrared predissociation of van der Waals cluster as well as a recent theoretical analysis of (C/sub 2/H/sub 4/)/sub 2/ dissociation.

• Research Organization: University of California, Los Alamos National Laboratory, Chemistry Division, Los Alamos, NM 87545
• OSTI ID: 6301653
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 78:12; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640302* -- Atomic
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
AGGLOMERATION
ALKENES
CHEMICAL REACTIONS
DECOMPOSITION
DIMERS
DISSOCIATION
ELECTROMAGNETIC RADIATION
ETHYLENE
HYDROCARBONS
INFRARED RADIATION
INTERMOLECULAR FORCES
MOLECULES
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PREDISSOCIATION
RADIATIONS
VAN DER WAALS FORCES