Minimum energy geometries, harmonic vibrational frequencies, and stepwise binding energies have been obtained for the cluster ions NO + ‚(H 2 O) n , n ) 1-4. From systematic ab initio calculations on the lighter NO + ‚(H 2 O) n complexes (n ) 1-2) at MPn, CCSD, and CCSD(T) levels of electron correlation with different basis sets, it was found that the MP2/6-311++G(2d,p) level of theory was reliable for the calculation of minimum-energy geometries and harmonic vibrational frequencies. Relative electronic energies were evaluated at the MP2/aug-cc-pVTZ//MP2/6-311++G(2d,p) level. The inclusion of zero point energy (ZPE) corrections, as well as counterpoise corrections for basis set superposition errors (BSSE), in the calculation of binding energies was essential to obtain the correct energy ordering for the different isomers of a cluster ion. The nature of the stepwise hydration processes was discussed based on the isomeric structures obtained. A reaction route for nitrous acid (HONO) formation when a water molecule is added to NO + ‚(H 2 O) 3 has been established.

He I photoelectron spectra have been recorded for the F + C 2 H 5 OH reaction, and a band has been identified associated with the primary reaction product CH 3 CHOH. The first adiabatic and vertical ionization energies of this radical have been measured as (6.64 ( 0.03) and ( 7.29 ( 0.03) eV respectively. The assignment of this band to CH 3 CHOH is supported by ab initio calculations performed at the G2 level of theory. Spectra recorded at different reaction times have demonstrated the short-lived nature of CH 3 CHOH and the major pathway of the F + C 2 H 5 OH reaction. The value measured for the adiabatic ionization energy has allowed the heat of formation of CH 3 CHOH to be derived from the heat of formation of CH 3 CHOH + .

The thermal decomposition of 2-H-heptafluoropropane, CF(3)CHFCF(3), at low pressure, heavily diluted in argon, has been studied over the temperature range 600-2000 degrees C using photoelectron spectroscopy. Comparison of the results obtained has been made with results of recent electronic structure calculations of possible decomposition pathways and results of a shock tube study. The most favored reaction thermodynamically, to produce CF(3)CF=CF(2) + HF, is found to be the main decomposition reaction at lower temperatures, 600-900 degrees C. At higher temperatures, 900-1200 degrees C, the decomposition reaction to give C(2)F(4) + CF(3)H was found to become important. No evidence for CF(3)CHFCF(3) --> CF(3)CHF + CF(3), a reaction expected to be important from a shock tube study, performed at much higher pressures, or for CF(3)CHFCF(3) --> CF(3)CF + CF(3)H was obtained, although for the latter reaction it is likely that CF(3)CF converts into C(2)F(4) under the conditions used before photoionization, in the ionization region of the photoelectron spectrometer. At higher temperatures C(3)F(6) decomposes to C(2)F(4) + CF(2), and C(2)F(4) decomposes to CF(2). Ab initio calculations have been performed of the adiabatic and vertical ionization energies of possible primary pyrolysis products to assist assignment of the photoelectron spectra recorded for heated flowing gas samples. A comparison is made between the threshold photoelectron spectrum and the photoelectron spectrum of CF(3)CF=CF(2).

The reaction OH -+ CH 2 F 2 f products has been investigated by both selected ion flow tube (SIFT) experiments and ab initio molecular calculations. The SIFT experiments showed that a bimolecular process, leading to two major anionic products, CHF 2 -(86%) and F -(11%), and one minor anionic product, HF 2 -(3%), is in competition with a three-body association leading to OH -‚CH 2 F 2 (where values in parentheses are the relative values of the detected anionic products at 300 K). From a pressure dependence study, an upper limit of the bimolecular reaction rate coefficient at 300 K is determined to be (2.4 ( 1.4) × 10 -12 cm 3 molecule -1 s -1 . This shows a small negative temperature dependence, suggesting that the reaction proceeds via an ion-complex intermediate. These experimental results were rationalized using ab initio molecular orbital calculations. Stationary points on the reaction paths of the two main reaction channels were located at both the HF/6-31++G ** and MP2/6-31++G ** levels. The relative energies of the located stationary points were calculated at up to the CCSD(T)/6-311++G 3df,2p //MP2/6-31++G ** level. The CHF 2 -+ H 2 O channel was found to be endothermic by 7.5 kcal mol -1 and the F -+ CH 2 (OH)F channel was found to be exothermic by 20.4 kcal mol -1 . It was found that both reaction channels proceed via the reactant-like ion-molecule complex intermediate, OH -‚CH 2 F 2 , in agreement with the conclusion drawn from the experimental negative temperature dependence of the overall rate coefficient. The fact that the product anion yields show that [CHF 2 -] > [F -], despite the fact that the CHF 2 -+ H 2 O channel is endothermic whereas the F -+ CH 2 (OH)F channel is exothermic, has been rationalized using transition-state theory.

1995 cleavage reactions, decomposition reactions, pyrolysis cleavage reactions, decomposition reactions, pyrolysis O 0100 40 -059 A Study of the Reactions of Molecular Fluorine with CH3SCH3 and CH3SSCH3 with UV Photoelectron Spectroscopy: First Observation of the HFCS Molecule -(gas-phase reaction; mechanisms; calculation of the ionization energies). -(BAKER, J.; BUTCHER, V. A.; DYKE, J. M.; LEE, E. P. F.; J.

It has been revealed by ab initio calculations at various levels that electropositive substituents (Li, BeH, and BH2) on silacyclopropene do not form bridge bond over the ring, as in the case of 1-BH2-phosphirene. Although in 1-lithiumsilacyclopropene Li occupies a position on the top of the ring, this structure, however, should be more appropriately described as a silacyclopropene anion Li+ ion pair, as shown by the MOs and Wiberg indices. For the various substituted thiirenes studied (with all combinations of the substituents Li, BeH, and BH2), instead of having a hypervalent sulfur, bridge bond structures (over the CC bond) are formed in all cases. For BeH,BH2-thiirene, the two substituents might position “above” or “behind” the ring, resulting in three different stable structures, and the most stable one has BeH forming a cage structure with the SCC ring. This bridge bond structure is similar to that in 1-BH2-phosphirene. Except for the case of having two BH2 groups, this cage structure has been found for all other substituent combinations. For this structure with two different substituent groups, the isomer with the more electropositive substituent group on the top of the ring is more stable. The bridge bond could be characterized by the participating AOs in both the highest doubly occupied a‘ and a‘‘ orbitals. Unlike in the case of 1-BH2-phosphirene, where dynamic electron correlation was needed to stabilize the bridge bond structure, the MO interaction alone was shown to be enough for the stabilization of this structure for the substituted thiirenes considered in this work.