Production of atomic oxygen following flash photolysis of ClONO2

The photodissociation of ClONO₂ using a broad-band ultraviolet photolysis source has been investigated using time-resolved atomic absorption spectroscopy in the vacuum ultraviolet. The predominant atomic photolysis product is O(³PJ), the quantum yield for Cl(²PJ) production being less than 4%.     

Differential cross section measurements of rainbow structure in Li+-Ar,Kr and Xe

The differential elastic cross sections (θ_lab < 20°) for Li⁺-Ar, Kr, Xe have been measured for 3 <E_c.m. < 9 eV and compared with those predicted from the electron gas theory of Gordon and Kim for closed shell systems. The experimental well depths are typically deeper than predicted by theory. The largest discrepancy of 9% was found for Li⁺-Kr.     

Triplet excition emissions of octafluoronaphthalene crystalline complexes with naphthalene and durene

The phosphorescence spectra of naphthalene-octafluoronaphthalene and durene-octafluoronaphthalene at 4.2 K reveal a localized exciton emission from octafluoronaphthalene, a weak intercomponent triplet-states quasi-resonance and a weak exciton-phonon coupling.     

On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.     

S42+ and S42− : an ab initio study

The structures of S₄²⁺ and S₄^2? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S₄^2? was also investigated. The anti chain form of S₄²⁺ was found to be 78.3 kJ mol^? more stable than the square form, in contrast to previous experimental data. S₄^2?is predicted to adopt the chain structure with the anti conformation.     

The absorption spectrum of 4,4'-dimethyldiphenylmethylene dm 4,4'-dimethylbenzophenone crystals

A polarized absorption study of the low-lying excited triplet states of 4,4'-dimethyldiplicnylmethylene dispersed in single crystals of 4,4'-dimethylbenzophenone at 4.2 K is presented. Polarization measurements of the visible absorption spectrum, commencing at 4841.7 A. yield an electronic configuration of (pσ)¹ (π^*)¹ for the first cxcited triplet state. A second cxcited triplet state, (pπ)¹ (π^*)¹, lies ≈ 800 cm^?1 above this.     

Homoisopavinanes—a highly probable class of phenethylisoquinoline alkaloids

Homoisopavinanes have been prepared by acid-catalysed cyclisation of the appropriately substituted aminoacetaldehyde dimethylacetal derivatives. The characteristic mass spectral fragmentation patterns of these homoisopavinanes is described.     

Induced changes in stimulated Raman scattering intensities

The stimulated Raman scattering (SRS) intensity of neat liquids and of binary liquid mixtures was measured as a function of the power of the pump field and of an additional radiation field at the Stokes frequency. In neat p-xylene SRS intensity transfer, form one vibrational mode to another, was observed. In benzene/nitrobenzene mixtures it was found possible, at various concentrations, to selectively generate SRS from one component in the mixture, including the minor one. Implications of the results for the selective excitation by the SRS process of a single species in a mixture are discussed.     

Resonance energy transfer between lasing dyes in micellar media

The photophysical behaviour of rhodamine 6G and coumarin 1 has been studied in a range of aqueous micellar media. Resonance energy transfer is demonstrated in dilute (10^?5 M) solutions and the location of the dye molecules in the micelle deduced from fluorescence lifetimes. A highly efficient, energy transfer dye laser is reported for dyes in micellar matrices.     

Vibronic effects in elastic scattering of electrons

A method for obtaining general equations for the scattered intensities from vibronic systems is given. The approximate formulas obtained are used to calculate the effects on the electron diffraction pattern for molecules with doubly degenerate electronic E terms interacting with e-type vibrations (Ee-type of problem). The results of the approximate calculations are compared to more precise results, based on numerical solution of the vibronic problem.     

Evidence for a Ag adatom-molecule complex in surface enhanced raman scattering

The SERS spectrum of molecules adsorbed on Ag sols show, lines, in the 200–300 cm^?1 region in the absence of Cl^? ions These lines are attributed to a Ag-N complex and frequency calculations show that they correspond to the vibrations of the molecule bound to a single silver atom.     

31P Solid state NMR geometrical effects on the chemical shift tensor

The principal components of the ³¹P chemical shift tensor σ of four cyclic organophosphorus compounds of different size, where the phosphorus atoms have the same chemical environment are reported from solid state NMR studies. The σ tensors show a large anisotropy. The asymmetry parameter η shows a linear variation as a function of the intracyclic bond angle around the phosphorus.     

A statistical model for the fragmentation of benzene by multiphotoionization

A statistical products phase space model for the (multi) photon fragmentation/ionization of polyatomic molecules in strong laser fields is proposed and tested on benzene. The mechanism assumes multiple dissociations and branchings starting with energy rich benzene ions. Calculated and experimental fragment mass patterns versus laser fluence are shown to be in good agreement.     

The wavefunction of non-stationary states in terms of complex coordinates and a related variational principle

The wavefunction of a decaying state is expressed in terms of complex coordinates as ψ(p) = a(θ)ψ _o(p) + b(θ)x(p), where the square integrable θ_o(p) and x(p) contain the localized and asymptotic information respectively. From Fano theory, we derive the relationship of a(?) and b(?) to the energy and width of the resonance state. This forms the basis for a new variatfonal principle for optimization of trial functions in the complex coordinate—energy plane.     

Electronic absorption spectroscopy of cooled supersonic expansions: dynamics of the 1B1u state of trans-butadiene

An ultraviolet absorption technique is developed for studying molecules cooled in a supersonic expansion. In this experiment, the temperature-dependent contribution to the diffuseness of electronically excited states is reduced for CS₂ and butadiene. The broadness of the spectral features of the butadiene ¹B_1u state is independent of temperature     

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol and the conformation of bicyclo[3.3.3]undecane (manxane)

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol has been determined. It is monoclinic, P2₁/c, a = 12.99(2), b = 14.16(2), c = 12.50(1)A,β = 112.42(2)°, with two independent molecules in the asymmetric unit. One of these is disordered, but the other has almost exact C_3h symmetry and its conformation and precise molecular geometry agree well with previous calculations by molecular mechanics. The molecule shows considerable angle strain, having bridge angles in the range 118–121°     

Franck-condon factors for I2 lines arising from Ar, K and He-Ne laser excitation

We report Franck-Condon factors for the I₂ B → X transitions excited by several lines of Ar⁺, Kr⁺ and He-Ne lasers and observed in fluorescence. The most recent and accurate molecular constants of Luc have been used in the calculation.     

1,2-Dihydroisoquinolines—XXI: Vinylogous meerwein salts

Treatment of 4-acyl-1,2-dihydroisoquinolines with the Meerwein reagent (triethyloxonium tetrafluoroborate) produces vinylogues of the ethoxyimminium cations in high yield. With a view to developing syntheses of 3-substituted isoquinoline derivatives, some reactions of these salts with nucleophilic reagents have been examined.     

Dibenz[de,g]isoquinoline derivatives—I

The oxidation of certain derivatives of 2-methyl-4-benzyl-1,2,3,4-tetrahydroisoquinoline with VOF₃ results in the formation of dibenz[de,g]isoquinolines in moderate to good yields, thus making these substances available for the first time.     

Rotationally resolved photoelectron angular distributions for H+2(ν′ = 0) at λ = 584 and 736 Å

The photoelectron asymmetry parameter for H⁺₂(ν′ = 0) was measured for the S rotational branch at λ = 584 and 736 Å using supersonic beam of n-H₂. Comparison with the theoretical β values of Itikawa demonstrates the importance of coupling between the p and f photoelectron waves at higher photon energy.