The electronic emission spectrum of benzaldehyde vapour

The electronic emission spectrum of benzaldehyde vapour excited in a discharge consists mainly of ã³A″-X?¹A′ phosphorescence but also contains some weak ùA″-X?¹A′ fluorescence. The spectrum has been photographed under high resolution with a view to establishing which a″ vibrations are active in the ã-X? system. We have shown, with the help of rotational band contours, that the vibration in which the substituent as a whole moves out-of-plane is weakly active and that the substituent torsional vibration is more weakly active. These are the only a″ vibrations which are active with sufficient intensity to be observed in the spectrum.In the Ã-X? fluorescence an a″ wagging vibration of the hhydrogen atoms of the phenyl ring is moderately strongly active, as is the corresponding excited state vibration in the Ã-X? absorption system     

A new transient absorption spectrum observed in the flash photolysis of thiophene

In the flash photolysis of thiophene diluted with argon, a transient absorption spectrum in the region 3770 Å and 4170 Å has been observed. The new absorption spectrum which consists of about 30 narrow and sharp red degraded bands could be analysed into an electronic system with the origin band at 4113.8 Å. The bands could tentatively assigned to the C₄H₃ radical.     

A new electronic transition in the polarized spectrum of dimethyl aniline

A new transition recently suggested at 265 nm in dialkyl anilines is confirmed by linear dichroism in an oriented matrix.     

A comment on the vibrational distribution of CO produced by the reaction of O with CS and CS2

There have been several meaurements of the CO vibrational distribution fromthe reaction of O with CS; these distributions differ significantly for vibrational levels below μ = 6. The differences can be reconciled by considering, via surprisal analysis techniques, the contribution of CO production from O + CS₂.     

A new satellite in the L-X-ray emission spectrum of tungsten-74

Using a 40 cm curved mica crystal spectrograph of the transmission type, the existence of a high frequency satellite at λ = 1268.84 X.U. in the L-emission spectrum of tungsten has been established for the first time. Based on the multiple ionisation theory, the satellite has been assigned to the transition L₂M₄ → M₄². According to the satellite nomenclature scheme proposed by Nigam and Mathur, this satellite would be designated Lβ₁₄.Kaufman's observation of a line at 1270.2 X.U. and its assignment to the octupole transition has been critically examined.     

Potential energy surfaces for the molecular and free radical dissociations of H2CS,F2CS and Cl2CS: An ab initio SCF MO study

Energies along the planar symmetric (C_2v) and planar assymetric (C_s paths to molecular dissociation of the ground state thiocarbonyl halides, F₂CS and Cl₂CS, together with their transition state geometries, have been calculated by ab initio SCF MO methods using the STO-3G and 4-31G basis sets. For comparison, results on H₂CS at similar levels of calculation are also included in this report. In addition, the 4-31G^** basis set has been employed to predict the geometries of the ground state species and the endothermicities of their free radical dissociations. The results of experiments in which the lowest excited singlet states of these molecules have been photoexcited are interpreted in light of these calculations. Thermodynamic data for both molecular and free radical dissociations are evaluated and discussed.     

A chemically pumped CO2 laser from the CS2O2 reaction

A chemical laser has been constructed in which simultaneous output is obtained from both CO and CO₂ laser species at 5 and 10 μm, respectively. Excitation of CO₂ is via energy transfer from vibrationally excited CO (CO²) produced in the photolytically initiated reaction: O + CS → CO² + S. Gain measurements at the CO₂ laser frequencies are also reported.     

Theoretical study on the vertical electronic spectrum of carbonyl fluoride,F2CO

Ab initio self-consistent-field (SCF ) and configuration interaction (CI ) calculations on the ground and excited states of carbonyl fluoride (F₂CO) were carried out at its experimental ground-state equilibrium geometry. Vertical transition energies deduced from the CI results provide assignments for the electronic systems I–IV, experimentally observed by Workman and Duncan. The singlet excited state, ¹A₁ (π→π*), is found to be a mixed valence–Rydberg state and to he 1 to 1.2 eV above the suggested experimental value, irrespective of the choice of the basis used for the CI calculations.     

A new parametrizable model of molecular electronic structure

A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the parametrization procedure--making a direct link to the correlated wavefunction theory. The model has been trained for 15 elements (H, Li-F, Na-Cl, 720 parameters) on a set of 5581 molecules (including ions, transition states, and weakly bound complexes) whose first- and second-order properties were computed by the coupled-cluster theory as a reference, and a good agreement is seen. The model looks promising for the study of large molecular systems, it is believed to be an important step forward from the traditional semiempirical models towards higher accuracy at nearly as low a computational cost.     

Dielectronic recombination in the zinc spectrum observed in inductively coupled plasma atomic emission spectroscopy

Observation of lines obtained through dielectronic recombination is illustrated in the case of zinc with an argon ICP as an excitation source. Several such lines are observed in the range of 200–300 nm. Due to large autoionization probability, some lines have a width around 0.1 nm. Information concerning other Zn lines observed in the same wavelength range is also provided.     

Bias effects on the electronic spectrum of a molecular bridge

In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level.     

The molecular structure and a Renner-Teller analysis of the ground and first excited electronic states of the jet-cooled CS2 + molecular ion

The A 2Pi(u) - X 2Pi(g) electronic band system of the jet-cooled CS2 + ion has been studied by laser-induced fluorescence and wavelength-resolved emission techniques. The ions were produced in a pulsed electric discharge jet using a precursor mixture of carbon disulfide vapor in high-pressure argon. Rotational analysis of the high-resolution spectrum of the 2Pi32 component of the 0(0) 0 band gave linear-molecule molecular structures of r0" = 1.5554(10) A and r0' = 1.6172(12) A. Renner-Teller analyses of the vibronic structure in the spectra showed that the ground-state spin-orbit splitting (A = -447.0 cm(-1)) is much larger than that of the excited state (A = -177.5 cm(-1)), but that the Renner-Teller parameters are of similar magnitude and that a strong nu1 - 2nu2 Fermi resonance occurs in both states. Previous analyses of the vibronic structure in the ground and excited states of the ion from pulsed field-ionization-photoelectron data are shown to be substantially correct.     

A new eletronic spectrum of the SiH3 radical observed using multiphoton ionization spectroscopy

The silyl radical, SiH₃, was observed between 365 and 410 nm using resonance-enhanced multiphoton ionization spectroscopy. The spectrum arises from two-photon resonance states which lie between 49229 and 54014 cm⁻¹. A vibrational progression interval of ≈ 800 cm⁻¹ was assigned to the resonant intermediate state symmetric deformation mode, ν₂.     

A crossed molecular beam study on the dynamics of F atom reaction with SiH4

In this report, the dynamics of the F+SiH4 reaction has been studied using the universal crossed molecular beam method. Angular resolved time-of-flight spectra have been measured for all reaction products in a single set of experiments. Two different reaction channels have been observed: HF+SiH3 and SiH3F+H. Product angular distributions as well as energy distributions were determined for these two product channels. Experimental results show that the HF product is forward scattered relative to the F atom beam direction, while the SiH3F product is backward scattered relative the F atom beam direction, suggesting that two reaction channels proceed with distinctive reaction dynamics. The relative branching ratios of the two channels have also been estimated.     

Chemiluminescent reaction of Al2 with F2

The reaction of Al₂ with F₂ is shown to proceed in a single collision to yield one AlF product in high Rydberg states and one in the ground state with a large cross section.     

A study of the reaction O + CS2 → SO + CS using crossed molecular beams

Measurements of SO scattering from the reaction O + CS₂ → SO + CS using crossed thermal molecular beams show that (a) there is strong forward sca     

Crystal structure of a new molecular complex of fullerene with tetramethyltetraselenafulvalene: C60·TMTSF·2CS2

A new molecular complex of fullerene with tetramethyltetraselenafulvalene (TMTSF), C₆₀·TMTSF·2CS₂, (1) was synthesized. The structure and composition of the complex were established by X-ray diffraction analysis. The crystals of C₆₀·C₁₀H₁₂Se₄·2CS₂ are monoclinic:a=15.407(2),b=12.934(2),c=12.026(2) Å β=108.39(3)°,V=2274.1(6) ų, space groupCm, Z=2,d _calc=1.929 g cm^?3,R=0.047. The crystal structure of 1 consists of layers. Layers formed by fullerene and CS₂ molecules alternate with layers of TMTSF molecules. Peculiarities of the crystal structure of 1 are the nonplanar conformation of TMTSF molecules and the absence of shortened C…C contacts between adjacent fullerenes molecules. The energy of intermolecular TMTSF…C₆₀ interactions in the crystal was estimated.