Comparison of models for treating angular momentum in RRKM calculations with vibrator transition states. Pressure and temperature dependence of Cl + C[sub 2]H[sub 2] association

Journal Article · Thu Jan 14 00:00:00 EST 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100104a010· OSTI ID:6390100

Zhu, L; Chen, W; Hase, W L ^[1]; Kaiser, E W ^[2]

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1. Wayne State Univ., Detroit, MI (United States)
2. Ford Motor Comp., Dearborn, MI (United States)

The RRKM expression for the microcanonical unimolecular rate constant depends on how the K rotational quantum number is treated. The limiting cases are to treat K as either adiabatic or active. The former occurs when K is a good quantum number for describing the vibrational/rotational energy levels. The latter case arises when coriolis coupling extensively mixes the (2J + 1) K levels. It is not necessary that K be simultaneously active or adiabatic for both the transition state and reactant molecule. Thus, four models which explicitly treat K with its proper limits, i.e.[minus]J[le]K[le]J, can be formulated for the RRKM theory. For example, to fit the association rate constant at low pressure using the model with K adiabatic in the transition state and active for the molecule requires a value for the collision efficiency [beta][sub c] twice the size needed when K is treated as active in both the molecule and transition state. These results indicate that until the proper model for treating K is identified it will be difficult to determine unambiguous values for [beta][sub c] by fitting experimental data. To assist in interpreting the experimental kinetics for the Cl + C[sub 2]H[sub 2] [r arrow] C[sub 2]H[sub 2]Cl system, ab initio calculations were performed to determine the structure, vibrational frequencies, and energy for C[sub 2]H[sub 2]Cl. The ab initio G2 value for the O K heat for Cl + C[sub 2]H[sub 2] association is [minus]16.855 kcal/mol. To fit the low-pressure experimental rate constants for Cl + C[sub 2]H[sub 2] association in air requires values for [beta][sub c] which range from 0.4 to 1.0. However, none of the RRKM models for treating K provides an adequate fit to all the temperature- and pressure-dependent experimental rate constants. 86 refs., 9 figs., 4 tabs.

• OSTI ID: 6390100
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 97:2; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ETHYLENE
CHEMICAL REACTION KINETICS
RADICALS
ANGULAR MOMENTUM
COUPLING
DISSOCIATION
ENERGY LEVELS
MATHEMATICAL MODELS
QUANTUM NUMBERS
REACTION HEAT
ROTATIONAL STATES
TEMPERATURE DEPENDENCE
VIBRATIONAL STATES
ALKENES
ENTHALPY
EXCITED STATES
HYDROCARBONS
KINETICS
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
THERMODYNAMIC PROPERTIES
400201* - Chemical & Physicochemical Properties