Yueshu Gu

Density functional study of the hydrogen bonding: H2O·HO

Abstract Density functional theory was used to study the hydrogen bonding between the water molecule and the hydroxyl radical. The two energetically low-lying minima are 1 ( 2 A ′ ) and 2 ( 2 A ″ ), with hydrogen bonding occurring between the oxygen atom of H 2 O and the hydrogen atom of the OH radical. Another hydrogen bond ( 3 , 2 A ″ ) occurs between one of the hydrogen atoms of H 2 O and the oxygen atom of OH. The interaction energies for various isomers were calculated at the UB3LYP, UMP2 and CCSD(T) levels. The infrared spectra and the vibrational frequency shifts are also reported.

AB INITIO POTENTIAL ENERGY SURFACE FOR THE REACTION OF O(3P) WITH CH2F

Abstract The potential energy surface (PES) for the reaction of an oxygen atom with a fluorinated methyl radical has been studied using the G2MP2 level of theory. The calculations reveal an association–elimination mechanism. The addition reaction of O( 3 P ) to CH 2 F produces an energy-rich intermediate OCH 2 F ∗ which subsequently decomposes irreversibly. Five production channels of OCH 2 F ∗ are found: H+CHFO, HF+HCO, CHFOH, F+CH 2 O and H 2 +FCO. CHFOH can decompose through six production channels: H+CHFO, HF+HCO, H+HCOF, H 2 +FCO, F+HCOH and OH+CHF. Based on the present ab initio PES, the kinetic characteristics of the O( 3 P )+CH 2 F reaction are estimated. The energy-specific rate constants for the unimolecular decomposition of OCH 2 F are calculated by RRKM theory. H+CHFO are predicted to be the major products.

Existence of hydrogen bonding between the hydroxyl radical and hydrogen peroxide: OH·H2O2

Abstract The hydrogen bonding between the OH radical and the H 2 O 2 molecule has been studied using ab initio molecular orbital methods. The OH·H 2 O 2 complex has a five-membered ring like structure with two distorted hydrogen bonds. The vibrational spectrum is reported. The binding energy D 0 of the OH·H 2 O 2 complex is predicted to be ∼4.1 kcal/mol.

WATER-CATALYZED MECHANISM FOR THE PYROLYSIS OF FORMIC ACID

Abstract The water-catalyzed mechanism for the pyrolysis of formic acid was studied by the ab initio quantum chemical calculations. The dehydration and decarboxylation reactions of formic acid occur via five- and six-member-ring hydrogen bonding complexes and transition states, respectively. The role of the water molecule is to serve as a proton relay acting simultaneously as a hydrogen-atom donor and acceptor. The corresponding potential energy surface was obtained at G2(MP2) level of theory. The large scatter in the reported experimental activation barriers for the dehydration and decarboxylation reaction of formic acid was explained reasonably.

Mechanism and rate constant of the reaction of atomic hydrogen with propyne

The potential energy surface for the reaction of atomic hydrogen with propyne has been studied at the G3//UB3LYP/6-31G(d) level of theory. Three reaction entrances were revealed, namely, terminal addition, nonterminal addition, and direct H-abstraction, leading to CH3CCH2, CH3CHCH, and H2+C3H3, respectively. The respective activation barriers are 1.7, 3.9, and 8.4 kcal/mol. The CH3-extrusion from CH3CHCH forms C2H2 via a barrier of about 32 kcal/mol. Several H-shift paths along the CCC skeleton were also examined for three C3H5 isomers. Multichannel RRKM and TST calculations have been carried out for the total and individual rate constants over a wide range of temperatures and pressures. The total rate constants possess both positive temperature dependence and typical “S” shaped fall-off behavior. At atmospheric pressure, the collisional stabilization of the initial adducts dominates the H+CH3CCH reaction at temperatures lower than 500 K, and at T>1000u200aK, CH3 and C2H2 are the major products. Moreover, the...

Mechanism of the OH+CH2CO reaction

Potential energy surface for the reaction of hydroxyl radical with molecular ketene has been studied using n the ab initio n G3(MP2) method. Three distinct reaction mechanisms, namely direct hydrogen abstraction, olefinic n carbon addition, and carbonyl carbon addition, are revealed. A total of seven primary product channels, H2O+HCCO, CO+CH2OH, HCO+CH2O, H+(HCO)2, H+CH(OH)CO, CO2+CH3 and CO+CH3O, including the consideration of six intermediates, are detailed. Moreover, the branching ratios are calculated using the RRKM-TST procedure. The findings in this theoretical study are in agreement with the available experimental measurements. The calculations show that at higher temperatures the major product channel is direct hydrogen abstraction leading to H2O and HCCO, whereas the formation of CO and CH2OH dominates the title reaction at lower temperatures.

Theoretical study of the hydrogen bonded structures between H2S and OH radical

Abstract The hydrogen bonding between the H 2 S molecule and the OH radical was studied for the first time using the UMP2 and UB3LYP methods with various basis sets. A total of three low-lying minima were found: 1 , H 2 S⋯HO ( 2 A′ state); 2 , H 2 S⋯HO ( 2 A″ state); and 3 , HSH⋯HO ( 2 A″ state). The infrared spectra for these structures were also reported. The structure 1 is predicted to be the global minimum, with a binding energy of about 7.0xa0kJxa0mol −1 calculated at CCSD(T)/6-311++G(2d,2p) level.

Theoretical investigation of the reactions of O(3P) with CH3F and CH2F2

Abstract The reactions of O( 3 P ) with CH3F and CH2F2 have been studied using ab initio G2(MP2) theory. The direct hydrogen abstraction mechanism was revealed for the first time. Two nearly degenerate transition states (of 3 A ″ and 3 A ′ symmetries) were located for each reaction. The rate constants and the equilibrium constants of two reactions were also predicted over a wide temperature range of 200–3000 K. Comparison of theoretical calculations with the limited experimental results were made and discussed.

Direct ab initio and kinetic calculation for the abstraction reaction of atomic O (3P) with CH3Br

Abstract The hydrogen abstraction reaction of O ( 3 P ) with CH 3 Br has been studied theoretically for the first time. Two nearly degenerate transition states of 3 A ″ and 3 A ′ symmetries have been located for this abstraction reaction. Geometries have been optimized at the UMP2 level with the 6-311G(2d, p) basis set. The G2MP2 method has been used for the final single-point energy calculation. On the basis of the ab initio data, the rate constants have been deduced over a wide temperature range 200–3000 K using canonical variational transition-state theory (CVT) with a small curvature tunneling effect (SCT). The calculated CVT/SCT rate constants exhibit typical non-Arrhenius behavior, a three-parameter rate-temperature formula is fitted in units of cm 3 molecule −1 s −1 as follows: k ( T )=(2.83×10 −19 ) T 2.33 exp(−2115.97/ T ).

Features of the potential energy surface for the decomposition of CH3OF

Abstract The G2MP2 theoretical procedure is used to calculate the potential energy surface for the decomposition of methyl hypofluorite (CH 3 OF). Geometries, vibrational frequencies and relative energies for the various stationary points have been obtained. The theoretical heats of reaction are in good agreement with the experimental values. CH 3 OF is stable with respect to the production of CH 3 O+F, CH 3 +OF, CH 2 +HOF and H 2 +HCOF, respectively, but unstable with respect to loss of HF and to isomerization. The major unimolecular decomposition channel of CH 3 OF involves the formation of HF and CH 2 O.