Understanding intramolecular energy flow in molecules is one of the central goals of chemical physics. Statistical theories [such as Rice-Ramsperger-Kassel-MarCus (RRKM) theory] of unimolecular reaction rates, which assume that the vibrational degrees of freedom rapidly exchange energy, have proved extremely successful (1). Recent work on small molecules has provided rigorous tests of these the...

The Whitten-Rabinovitch (WR) approximation used in the semi-classical calculation of the Rice-Ramsperger-Kassel-Marcus (RRKM) unimolecular reaction rate constant was improved for reliable application to protein reactions. The state sum data for the 10-mer of each amino acid calculated by the accurate Beyer-Swinehart (BS) algorithm were used to obtain the residue-specific correction functions (w...

Ab-initio methods were carried out to calculate forward and reverse rate constant data for the following reactions: HgþCl22HgCl2, HgClþCl2HgCl2, HgþO2HgO, and SeþH22SeH2. Theoretical predictions of bond distances, vibrational frequencies and enthalpies of reaction are compared to available experimental data to determine the level of theory most appropriate for predicting kinetic parameters. The...

The general approach to classical unimolecular reaction rates due to Thiele is revisited in light of recent advances in the phase space formulation of transition state theory for multidimensional systems. Key concepts, such as the phase space dividing surface separating reactants from products, the average gap time, and the volume of phase space associated with reactive trajectories, are both r...

The unimolecular dissociation and isomerization kinetics of the three methyl propanoate (MP) radicals, CH3CH2C(=O)OĊH2 (MP-m), CH3ĊHC(=O)OCH3 (MP-α), and ĊH2CH2C(=O)OCH3 (MP-β), are theoretically investigated using high-level ab initio methods and the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) theory. Stationary-point energies are obtained using the coupled cluster singles and do...

We investigate the oxidation of methacryloylperoxy nitrate (MPAN) and methacrylicperoxy acid (MPAA) by the hydroxyl radical (OH) theoretically, using both density functional theory [B3LYP] and explicitly correlated coupled cluster theory [CCSD(T)-F12]. These two compounds are produced following the abstraction of a hydrogen atom from methacrolein (MACR) by the OH radical. We use a RRKM master e...

A model is proposed for studying the reaction dynamics in complex quantum systems which complete mixing of states hindered by an internal barrier. Such are often treated transition-state theory, also known chemistry as RRKM but validity theory questionable when there no identifiable coordinate associated with The consists two Gaussian Orthogonal Ensembles (GOE) levels coupled to each other and ...

Infrared-ultraviolet hole-burning and hole-filling spectroscopies have been used to study IR-induced dissociation of the tryptamine.H2O and tryptamine.D2O complexes. Upon complexation of a single water molecule, the seven conformational isomers of tryptamine collapse to a single structure that retains the same ethylamine side chain conformation present in the most highly populated conformer of ...

Gao and Marcus (1) presented a modified Rice, Ramsperger, Kassel, Marcus (RRKM)– based theory to explain the strange and unconventional ozone isotope effect that has puzzled scientists for years. In earlier studies, mass spectrometric (2, 3) and diode laser (4) measurements of ozone isotopomers in “scrambled” oxygen mixtures pointed toward a symmetry origin for isotope fractionation. Kinetic st...

In this theoretical research, the mechanism of the C2H + C2H2 reaction is studied by high-level quantum-chemical methods and kinetics of the reaction is investigated by statistical rate theories. High-level electronic structure calculation methods including M06-2X, CCSD(T), CBS-Q and G4 methods are employed to explore the doublet potential energy surface of the reaction and compute the molecula...