Showing papers by "Bruce S. Ault published in 2004"

Matrix Isolation Infrared Spectroscopic and Theoretical Study of the Interaction of Water with Dimethyl Methylphosphonate

Abstract: Matrix isolation infrared spectroscopy has been combined with theoretical calculations for the characterization of the 1:1 hydrogen-bonded complex between H 2 O and dimethyl methylphosphonate (DMMP). The symmetric O-H stretching mode was observed to shift 203 cm - 1 to lower energy upon hydrogen bond formation, while a 32 cm - 1 blue shift was noted for the H-O-H bending mode of the H 2 O subunit in the complex. These values compare extremely well with the (unscaled) shifts of -203 and +32 cm - 1 , respectively, that were calculated theoretically at the MP2/6-31+G** level. Additional perturbed modes of the DMMP subunit were observed, shifted relative to the parent band position. The greatest perturbation was to the P=O stretching mode near 1270 cm - 1 , where a shift of -17 cm - 1 was observed (-21 cm - 1 calculated theoretically). This suggests that the site of hydrogen bonding in the complex is at the P=O group, in agreement with theoretical calculations. The binding energy ΔE° for the 1:1 complex was calculated to be -7.7 kcal/mol.

Matrix Isolation and Theoretical Study of the Reaction of Ethyne with OVCl3 and CrCl2O2

Abstract: Infrared spectroscopy, coupled with matrix isolation and theoretical calculations, has been used to reexamine the photochemical reaction of C2H2 with CrCl2O2, as well as to extend the study to the ...

Matrix isolation study of the reaction of dimethyl sulfoxide with CrCl2O2 and OVCl3

Abstract: The matrix isolation technique, combined with infrared spectroscopy and theoretical calculations, has been employed to investigate the thermal and photochemical reactions of dimethylsulfoxide (DMSO) with CrCl 2 O 2 and OVCl 3 . Twin jet codeposition leads to formation and isolation of a photochemically unstable 1:1 complex. The photoproduct in the twin jet DMSO + CrCl 2 O 2 experiments is identified as dimethyl sulfone, (CH 3 ) 2 SO 2 , interacting with the Cl 2 CrO fragment, while in the analogous OVCl 3 reaction, the photoproduct bands were too weak to allow product identification. Merged jet codeposition led to rapid gas phase reaction, and in the case of DMSO + CrCl 2 O 2 , dimethyl sulfone is formed in high yield. This marks the first demonstration of a gas phase thermal oxygen atom transfer from CrCl 2 O 2 to an organic substrate. For the reaction of DMSO with OVCl 3 , no volatile products are deposited in the matrix and dimethyl sulfone is not a product. These results support differing pathways for the reactions of CrCl 2 O 2 and OVCl 3 , a conclusion that is supported by density functional calculations.

Matrix-Isolation Infrared and Theoretical Study of the Reaction of VCl4 with CH3OH

Abstract: The matrix isolation technique, combined with infrared spectroscopy and theoretical calculations, has been used to investigate VCl4, as well as its reactions with CH3OH and its isotopomers. The infrared spectrum of VCl4 in solid argon showed an intense doublet at 474 and 501 cm-1, which is indicative of a splitting of the triply degenerate stretching mode in Td symmetry due to Jahn−Teller distortion. Density functional theory (DFT) calculations (UB3LYP/6-311++g(d,2p)) reproduced this splitting very well. The calculated structure had four equal V−Cl bonds, but with two Cl−V−Cl angles equal to 110.8° and two angles equal to 106.9°. Using twin-jet deposition, the initial intermediate in the reaction of VCl4 with CH3OH was identified as a 1:1 molecular complex, characterized by perturbations to the V−Cl, C−O, and O−H stretching modes. This complex was destroyed by near-UV irradiation, producing the novel Cl3VOCH3 species and cage-paired HCl. Merged-jet co-deposition of CH3OH and VCl4, with a room-temperature ...

Matrix Isolation Infrared and Theoretical Study of the Reaction of VCl4 with NH3 and (CH3)3N

Abstract: Initial and secondary intermediates in the reaction of VCl4 with NH3 have been characterized by matrix isolation infrared spectroscopy and density functional calculations. Twin jet codeposition of these two reagents led to a series of moderately intense infrared absorptions that have been assigned to the 1:1 molecular complex between these two species. Irradiation of these matrices with light of λ > 300 nm led to complete destruction of the complex, and the growth of a number of new bands. These have been assigned to the Cl3VNH2 species, complexed with a single HCl arising from destruction of the complex. Identification of these species (1:1 complex and photoproduct) was supported by extensive isotopic labeling (15N and 2H), as well as by B3LYP/6−311++g(d, 2p) density functional calculations. Good agreement was observed between the experimental and computed frequencies. The binding energy of the 1:1 complex was calculated to be = −11.43 kcal/mol at this level of theory. Similar experiments with (CH3)3N le...

Theoretical Study of the Reaction Mechanism and Role of Water Clusters in the Gas‐Phase Hydrolysis of SiCl4.

Abstract: The energies and thermodynamic parameters of the elementary reactions involved in the gas-phase hydrolysis of silicon tetrachloride were studied using ab initio quantum chemical methods (up to MP4//MP2/6-311G(2d,2p)), density functional (B3LYP/6-311++G(2d,2p)), and G2(MP2) theories. The proposed mechanism of hydrolysis consists of the formation of SiCl 4-x(OH)x (x ) 1-4), disiloxanes Cl4-x(OH)x-1Si-O-SiCl4-x(OH)x-1, chainlike and cyclic siloxane polymers [-SiCl2sO-]n, dichlorosilanone Cl2SidO, and silicic acid (HO)2SidO. Thermodynamic parameters were estimated, and the transition states were located for all of the elementary reactions. It was demonstrated that the experimentally observed kinetic features for the hightemperature hydrolysis are well described by a regular bimolecular reaction occurring through a four-membered cyclic transition state. In contrast, the low-temperature hydrolysis reaction cannot be described by the traditionally accepted bimolecular pathway for SisCl bond hydrolysis because of high activation barrier (Ea ) 107.0 kJ/mol, ¢G q ) 142.5 kJ/mol) nor by reactions occurring through three- or four-molecular transition states proposed earlier for reactions occurring in aqueous solution. The transition states of SiCl 4 with oneand two-coordinated water molecules were located; these significantly decrease the free energy of activation ¢G q (to 121.3 and 111.5 kJ/mol, correspondingly). However, this decrease in ¢G q is not sufficient to account for the high value of the hydrolysis rate observed experimentally under low-temperature conditions.