Effective bending frequencies, energies, and tunneling parameters of transition states from thermal rate data and semiempirical internuclear distances: DHH, HDD, OHH, ODD

Journal Article · Thu Jul 16 04:00:00 EDT 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100299a038· OSTI ID:6137790

Furue, H; Pacey, P D

Three parameters of a transition-state theory expression have been fitted by nonlinear least squares to experimental data for four reactions: D + H/sub 2/ ..-->.. DH + H (1), H + D/sub 2/ ..-->.. HD + D (2), O + H/sub 2/ ..-->.. OH + H (3), and O + D/sub 2/ ..-->.. OD + D (4). The model incorporated a factor for one-dimensional tunneling through an Eckart barrier and a Pitzer-Gwinn partition function for bending in a potential consisting of two adjacent harmonic wells. Stretching motions were assumed to be in their ground states. Semiempirical internuclear distances and experimental reaction enthalpies were provided as input. The fitted parameters were the effective barrier height, E/sub e/, the effective, harmonic, transition-state bending term value, w/sub b/, and the characteristic tunneling temperature, T*, equal to hcw*/(2..pi..k/sub B/), where w* is the harmonic term value for a well with curvature equal but opposite to the barrier top. The fitted values of E/sub e/ agreed within 3 kJ mol/sup -1/ with the best estimates from ab initio calculations, providing evidence that transition-state vibrational zero-point energy does provide a real barrier to reaction and that vibrational anharmonicity is important for these reactions. Values of w/sub b/ from the model described above agreed with ab initio values for reactions 1, 3, and 4 within 310 cm/sup -1/ or 36%. Values for reaction 2 were less certain because of conflicts within the experimental data.

• Research Organization: Dalhousie Univ., Halifax, Nova Scotia
• OSTI ID: 6137790
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:15; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
CHEMICAL REACTIONS
DATA
DEUTERIDES
DEUTERIUM
DEUTERIUM COMPOUNDS
ELECTRONIC EQUIPMENT
ELEMENTS
ENERGY LEVELS
ENTHALPY
EQUIPMENT
EXCITED STATES
EXPERIMENTAL DATA
HARMONIC OSCILLATORS
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MECHANICS
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
OSCILLATORS
OXYGEN
PHYSICAL PROPERTIES
POTENTIALS
QUANTUM MECHANICS
REACTION HEAT
STABLE ISOTOPES
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
VIBRATIONAL STATES