摘要:

Abinitiocalculations were performed on several aquo complexes of NH2•, and NH3•+, and on monomeric parent species. The geometries were optimized at the HF/6-31 + G* level and the vibrational frequencies were calculated. The total energies and the binding energies of complexes were evaluated at the MP2/6-31 + G* + ZPE level of theory. Gas and aqueous solution phase thermodynamic properites of NH2•and NH3•+and several other species were calculated. The examination of solution phase properties of the radicals was facilitated by study of the structures and transition energies of aquo complexes. H-bonding interaction energies decreased in the orderbut were generally stronger than σ–σ* interactions involving the unpaired electron. From calculations with the CIS method, the weak absorption observed at 520 nm for aqueous NH2•is confirmed as a2B1 → 2A1transition, while the stronger NH2•absorption occurring below 250 nm and the absorption of NH3•+, which rises monotonically below 370 nm, are attributed to solvent-to-solute charge transfer bands. The solution free energies and relatedE0values for NH2•and NH3•+are in agreement with those of Stanbury. Theabinitiostructure studies show that water protons are bound to N, and proton transfer from solvent in reaction [18], NH2• + e− + H2O → NH3 + OH−, is likely to be the dominant redox reaction of NH2•in alkaline solution. The free energy of solution of NH3•+is shown to be larger than that of.

ISSN:0008-4042    

DOI:10.1139/v94-069

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Vibrational to translational energy transfer was studied computationally and analytically for collinear, impulsive collisions with square well oscillators, harmonic oscillators, and Morse oscillators. At a fixed temperatureTthe average number of encounters is between one and two if the vibrational energyEVis large compared tokTand (or) if the relative mass of the collider is small. If these conditions are met,the average energy transferred per collision, varies nearly linearly withEVover a wide range. If the average number of encounters is greater than two,as a function ofEVhas a more complicated form. The average final energy,is less than what is predicted by the single encounter impulsive collision (SEI) model. Other things being equal, the ratio of the actual average final energy to the SEI average final energy is roughly the same for all of the above mentioned oscillators.

ISSN:0008-4042    

DOI:10.1139/v94-070

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Electron localization in solids and liquids is caused by time-dependent perturbations of the media surrounding the charge. The perturbations active on the femtosecond time scale include electronic polarization, as well as intra and intermolecular vibrational excitations, which contribute to the formation of a potential well around the charge. It is shown that information on these perturbations as well as on femtosecond reactions can be obtained by studying the formation of transient anions in dielectric solids and at their surfaces using high-resolution electron beam techniques at low energies (0–20 eV). The results obtained with Ar, N2, O2, and organic thin solid films condensed on a Pt substrate are described.

ISSN:0008-4042    

DOI:10.1139/v94-071

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Molecular beam laser Stark spectroscopy has been used to measure the υ = 3 vibrational state dipole moment of hydrogen fluoride as 1.9614 ± 0.0021 debye. This measurement allows μυto be expressed as a power series expansion inwithout the use of infrared intensity data. A detailed comparison is made with similar series based mainly on infrared intensity data and more recentabinitiocalculation

ISSN:0008-4042    

DOI:10.1139/v94-072

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The experimental VCD spectrum of (2R)-2-methylaziridine has been measured in the region 800–1500 cm−1. Theabinitioimplementation of the Vibronic Coupling Theory (VCT) of Nafie and Freedman, using the 6-31G*(0.3)basis set, in the common origin and distributed origin gauges and with uniformly and optimally scaled quantum mechanical force fields, is used to investigate the chiroptical properties. VCD spectra are computed for bothcisandtransinvertomers. The predicted VCD spectrum of 2-methylaziridine (the equilibrium mixture) is dominated by that of thetransdiastereomer, not simply because of its greater abundance but because the rotatory strengths of many absorptions in the mid-IR are oppositely signed and of similar magnitude in the two invertomers which differ in absolute configuration at nitrogen. The VCD spectrum of 2-methylaziridine is compared in detail to that of 2-methyloxirane. In the region of the methyl group deformations and CH2scissor, the theoretical (R)-2-methyloxirane VCD spectrum displays a much closer similarity to thecis-(2R)-2-methylaziridine than to thetransdiastereomer.

ISSN:0008-4042    

DOI:10.1139/v94-073

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The carbon-13 chemical shifts of several substituted nitrosobenzenes are reported. It is shown that the NO group can be orientated to lie in the plane of the ring when constrained either by a bulkyorthosubstituent or in the solid state. In the presence of 2,6-di-tert-butyl substituents the NO group is twisted into orthogonality with the ring. The changes in the13C chemical shifts are larger for the NO group than for other functional groups. It is suggested that these effects are a consequence of the electronic character of the NO group and that the nitrogen lone pair of electrons is of fundamental importance in producing these unique effects. The dimeric nitroso functional group does not display these properties.

ISSN:0008-4042    

DOI:10.1139/v94-074

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Abinitiotheoretical computations have been performed for RhN2, Rh+N2, Rh(N2)2, and Rh+(N2)2species. The computed vibrational frequencies and binding-energy trends are in qualitative accord with prior FTIR studies of N2interacting with supported Rh films. Computations of the type described herein should be useful in aiding the assignment of observed infrared bands to specific surface species in future work.

ISSN:0008-4042    

DOI:10.1139/v94-075

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Reactive scattering of F atoms with Br2molecules has been studied at an initial translational energyE ∼ 16 kJ mol−1using a supersonic beam of F atoms seeded in Ne buffer gas. Laboratory angular and velocity distributions of BrF product have been measured. They show sharp peaking in the forward direction with almost isotropic wide angle scattering of relative intensity ∼ 0.2. Approximately half the total available energy is disposed into product translation for scattering in the forward and backward directions with slightly lower translational energy for the sideways scattering. The combination of sharp forward scattering and high product translational energy is attributed to early migratory trajectories in large impact parameter collisions whereby the F atom reacts with the more distant Br atom of the Br2molecule lying in the forward hemisphere. The isotropic wide angle scattering arises from direct trajectories in which the F atom reacts with the nearer Br atom of the Br2molecule. Migratory dynamics are promoted by charge transfer interaction of the form Br2+F−which stabilises the potential energy surface in elongated isosceles triangular FBr2configurations as well as in slightly bent FBrBr configurations. Comparison is made with the dynamics of the F + Cl2, I2, and CCl3Br reactions.

ISSN:0008-4042    

DOI:10.1139/v94-076

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Dipole (e,e) spectroscopy has been used to measure the absolute photoabsorption oscillator strengths (cross sections) for the valence shells of CH3NH2, (CH3)2NH, and (CH3)3N from the photoabsorption threshold to 250 eV at low resolution (∼1 eV fwhm) and to 31 eV at high resolution (0.048 eV fwhm). The observed peaks in the photoabsorption spectra of the methylamines have been assigned to transitions to Rydberg orbital upper states. Our measured photoabsorption data, augmented by mixture rule estimates for high photon energies, have been used in conjunction with Thomas–Reiche–Kuhn sum rule and molar refractivity constraints, to construct constrained dipole oscillator strength distributions for each of the methylamines. From these constrained dipole oscillator strength distributions a wide range of related dipole properties have been calculated for each of the methylamines, and in most cases the results so obtained represent the first (reliable) determination of these properties.

ISSN:0008-4042    

DOI:10.1139/v94-077

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The synthesis and properties of dihydrogen complexestrans-[MH(H2)L]+, M = Fe, Ru, Os, which contain the ligandmeso-tetraphos-1,S,R-Ph2PCH2CH2P(Ph)CH2CH2P(Ph)CH2CH2PPh2(L) are described. There are interesting possibilities of isomerism in suchtranscomplexes because the axial binding sites at the metal are different, one being surrounded by four phenyl groups and the other by two phenyl groups. The osmium complex is prepared in an unusual reaction ofcis-β-Os(Cl)2L with H2(1 atm) and NaBPh4(1 mol) in THF or by the reaction oftrans-OsH(Cl)L with NaBPh4and H2. The iron and ruthenium complexes were made by a reaction of HBF4with complexestrans-M(H)2L that have inequivalenttranshydrides. The ruthenium complex was also prepared starting from isomers oftrans-RuH(Cl)L. The H—H distance in the rapidly spinning dihydrogen ligand has been calculated fromT1(min) data to be 0.88, 0.89, and 0.99 Å for the complexes of Fe, Ru, Os, respectively. The presence of the H—D bond in the isotopomerstrans-[MH(HD)L]+andtrans-[MD(HD)L]+is also confirmed by the observation of1JHDcoupling constants of 32, 33.5, and 26.4 Hz for Fe, Ru, and Os, respectively. There is no rapid intramolecular H atom exchange in these complexes in contrast to those with di-tert-phosphine ligands like [MH(H2)(dppe)2]+or to the trihydride Re(H)3L. Described also are the properties of the precursor complexes includingcis-β- andtrans-Ru(Cl)2L and derivatives of the dihydrogen complexestrans-[MH(L′)L]+, L′ = CH3CN (on Ru and Os), PMe2Ph (on Ru), and CO (on Os). Trends in the NMR properties of isostructural complexes are reported.

ISSN:0008-4042    

DOI:10.1139/v94-078

出版商:NRC Research Press    

年代:1994

数据来源: NRC