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Influence on isotope effect calculations of the method of obtaining force constants from vibrational data

Journal Article · · J. Phys. Chem.; (United States)
DOI:https://doi.org/10.1021/j100394a014· OSTI ID:6819686
; ; ;

Reduced isotopic partition function ratios (s/sub 2//s/sub 1/)f are employed in the calculation of isotope effects on thermodynamic equilibrium constrants. The quadratic force constants of the molecular force field are needed to evaluate (s/sub 2//s/sub 1/)f. Often these force constants are directly deduced from observed fundamentals in vibrational spectra and the (s/sub 2//s/sub 1/)f values so obtained are labeled (ANHARM). In a theroretically more valid procedure that is more difficult, one corrects observed fundamentals for anharmonicity on the basis of observed overtone and combination bands and then deduces force constants from these observed harmonic frequencies. The (s/sub 2//s/sub 1/)f values obtained from these force constants are labeled (HARM). (HARM) values and (ANHARM) values are evaluated and the isotope effects calculated with these values are discussed. It is concluded that the consistent use of (ANHARM) values in such calculations is a valid procedure.

Research Organization:
Univ. of California, Irvine
DOE Contract Number:
AT03-76ER70188
OSTI ID:
6819686
Journal Information:
J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 86:5; ISSN JPCHA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
400302 -- Organic Chemistry-- Isotope Effects-- (-1987)
BORN-OPPENHEIMER APPROXIMATION
CALCULATION METHODS
CORRECTIONS
DEUTERIUM
ENERGY LEVELS
EQUILIBRIUM
EXCITED STATES
FUNCTIONS
HARMONIC POTENTIAL
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MEDIUM TEMPERATURE
NUCLEAR POTENTIAL
NUCLEI
ODD-ODD NUCLEI
PARTITION FUNCTIONS
POTENTIALS
STABLE ISOTOPES
THERMAL EQUILIBRIUM
VIBRATIONAL STATES