摘要:

The gas phase infrared and liquid phase Raman spectra of the title compounds have been recorded and vibrational analyses performed. The spectra show evidence for the presence in both the liquid and vapour phases of two rotational isomers:cisoid-Zandtransoid-Zwith reference to orientation of isocyanato and methyl groups relative to the carbonyl group.

ISSN:0008-4042    

DOI:10.1139/v93-203

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Oscillator strengths for C 1sexcitation of gas phase Cp2TiCl2and CpTiCl3(Cp = η5-C5H5), and Cl 2pand Ti 2pexcitation of gas phase Cp2TiCl2, CpTiCl3, and TiCl4have been derived from electron energy loss spectra recorded under electric dipole scattering conditions. The C 1sspectra are interpreted with the aid of semiempirical extended Hückel calculations and comparisons with the C 1sspectra of other cyclopentadienyl complexes. The Ti 2pspectra are interpreted using the extended Hückel results and comparisons with atomic multiplet–crystal field calculations for Ti4+taken from the literature.

ISSN:0008-4042    

DOI:10.1139/v93-204

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The 2880 Å system in the Tesla discharge spectrum of I2in Ar is reexamined using a CCD array detector to record spectra for both127I2and129I2. This charge-transfer transition terminates on a weakly bound valence state, giving a highly congested spectrum with fine violet-degraded band structure barely perceivable on a pseudocontinuous background. The superior signal-to-noise capabilities of the array detector permit a great improvement in the precision and number of measured bandheads, as compared with previous results obtained from photographically recorded spectra. The new data span a larger range of vibrational levels in the lower state and lead to a change in the previous ν″ numbering by −3 units. Both states can now be located precisely on the absolute energy axis through least-squares fits in which the lower state energy is represented as a near-dissociation expansion. The primary spectroscopic constants (cm−1) areThe lower state has a dissociation energy of 287.5 cm−1and supports 35 bound levels, subject, however, to possible further revision due to a remaining uncertainty of 1 unit in the ν″ numbering. The previous tentative electronic assignment of this system remains in effect: The upper state is likely thestate that correlates with I−(1S) + I+(3P1), while the lower state is thecomponent of the lowest valence3Πumultiplet.

ISSN:0008-4042    

DOI:10.1139/v93-205

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

An experimental and theoretical study is reported of the 600 nm band system of phenoxyl and several methoxy substituted phenoxyls. These radicals, generated in freon, show a diffuse band in this region with a vibrational structure that is incompletely resolved but consistent with the 500 cm−1 "progression" observed earlier for phenoxyl in the vapour and in a rigid matrix. The low intensity of this band is considerably enhanced byortho-methoxy substitution. To establish its assignment and analyze its structure, semi-empirical andabinitioquantum chemical calculations have been performed. It is found that, on the basis of the ordering of the states and the magnitude of their transition moments, all calculations favour a ππ* (2B2 → 2A2) rather than the earlier proposed nπ* assignment for this band. Of the methods used, only the (abinitio) CASSCF method is found to be able to simulate the observed vibrational structure adequately. This simulation is based on optimized structures and vibrational force fields calculated for the 1B2and 1A2states of phenoxyl. It identifies the dominant mode of about 500 cm−1as ν6athe characteristic deformation mode of phenyl rings, but shows that higher members of the "progression" receive large intensity contributions from higher frequency modes. The chosen assignment and the assignments of higher-energy transitions reported in the literature are compared with those for the better known benzyl radical. It is shown that some of the phenoxyl assignments reported in the literature contain errors.

ISSN:0008-4042    

DOI:10.1139/v93-206

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The "giant dipole" molecules, NR1R2—C6H4—(C≡C)n—C6H4—NO2n = 0, 1, 2, are studied theoretically for three sets of substituents: R1 = R2 = H, R1 = H, R2 = CH3, and R1 = R2 = CH3. For each of these nine molecules, the energies, and permanent and transition dipole moments for the 20 lowest electronic states are calculated using the intermediate neglect of differential overlap (INDO) approximation at the configuration interaction with single excitations (CIS) level. Static polarizabilities and hyperpolarizabilities for the ground states are reported for these "push–pull" molecules. The changes in the physical properties of interest due to increase in conjugation length and the inductive effect of substituents on the donor group attached to the rings are discussed. The energies and permanent and transition dipole moments for the ten lowest electronic states are tabulated for use in future studies of the spectral and dynamical effects of permanent dipoie moments on laser-induced one- and multi-photon electronic transitions in realistic models for many-level giant dipole molecules.

ISSN:0008-4042    

DOI:10.1139/v93-207

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The 353 nm vapour absorption of 4H-pyran-4-one, and its 3,5-d2derivative, has been measured and assigned to a forbidden,1A2(nπ*)–1A1electronic transition, with electronic origin near 28 360 cm−1, made allowed by vibrations involving out-of-plane ring and C—H motions. Although the molecule remains planar upon excitation, other effects of conjugation on the nature of the excited state are less marked than in 2-cyclopenten-1-one.

ISSN:0008-4042    

DOI:10.1139/v93-208

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The tetrakis(trimethylsilyl)ethynyl derivatives of Si, Ge, Sn, and Pb were prepared and examined spectroscopically. NMR and Mössbauer spectroscopy and X-ray crystal structure data clearly demonstrate an electronic interaction in the ground state between the distal SiMe3groups and the central metal atom, leading to a strong shielding of the central metal atom; the respective nmr signals of the central metal are among the most shielded examples reported for a tetrahedral Group 14 metal centre with four carbon ligands. The nature of these electronic interactions is discussed.

ISSN:0008-4042    

DOI:10.1139/v93-209

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

High resolution Fourier transform spectra of the ν5and ν8bands of CD3C≡CH have been recorded and analyzed taking into account the strongx–yCoriolis interaction between these fundamentals. Fermi resonance of the ν8state with the ν9 + ν10state,l-type doubling interaction between the ± lcomponents of ν8and a weakk-type doubling interaction between the ν5and ν8states have also been included in the perturbation treatment. The parameters of the ν5and ν8states as well as some of the parameters of the unobserved ν9 + ν10state have been determined. An estimate of the relative value of the transition moments has been obtained from the line intensities, which are strongly affected by thex–yCoriolis interaction.

ISSN:0008-4042    

DOI:10.1139/v93-210

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The (0200)Σ+ ← (000)Σ+, (0220)Δ ← (010)Π, (0200)Σ+ ← (010)Π, and (010)Π ← (000)Σ+bands in theelectronic system of SrOH have been recorded at Doppler limited resolution using CW dye laser excitation with selective detection. Fluorescence from selected rotational levels of theandvibronic states has been dispersed, providing access to the (0200)Σ+and (0220)Δ levels of the ground electronic state. Over 1200 line positions from all transitions were included in a global least-squares fit. The effects of a weak ℓ-type resonance between the ℓ = 0 and ℓ = 2 components of the ν2 = 2 vibrational level were observed in both electronic states and the off-diagonal matrix elements were evaluated in a case (b) basis. A previous analysis of thelevel that attributes the anomalous ℓ-type doubling to an electronic perturbation arising from thepolyad is inconsistent with our experimental

ISSN:0008-4042    

DOI:10.1139/v93-211

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The energy levels of the lower valence and Rydberg states of selenoformaldehyde, CH2Se, have been calculated by the SCF/CI method. Wavefunctions for the ROHF (restricted open shell Hartree–Fock) states were obtained with the Binnings–Curtis double-ζ basis set, augmented with Rydberg and polarization functions. Configuration interaction was applied to the parent configurations, PCMO (parent configuration molecular orbital). Oscillator strengths were evaluated for the allowed electric dipole transitions by the RPA (random phase approximation), and SOPPA (second-order polarization propagator approximation) methods. The spin-orbit contribution to the zero field splitting of the first triplet state,3A2(n,π*) as well as the oscillator strengths to the three spin components were calculated by perturbation theory. These calculations predict that theSx,Sy, andSzcomponents are shifted by −96.091,−96.707, and + 29.167 cm−1, respectively, from their unperturbed position. The oscillator strengths for the three componentsfx,fy, andfzof the3A2(n,π*) ← 1A1(g.s.) transition were calculated to be 3.45 × 10−7, 1.15 × 10−7, and 173.0 × 10−7.

ISSN:0008-4042    

DOI:10.1139/v93-212

出版商:NRC Research Press    

年代:1993

数据来源: NRC