Picosecond rotational diffusion by differential single-photon fluorescence spectroscopy

The rotational diffusion contants of rhodamine-6G, coumarin-1 and N-acetyltryptophanamide in various solvents have been determined by an experimental method where the vertically and horizontally polarized fluorescence spectra are measured simultaneously by the same detector. The results indicate that the Debye—Stokes—Einstein model does not hold for coumarin-1 and N-acetyltryptophanamide in ethylene glycol.     

Hybridization in propellanes

Using the Maximum Overlap Approximation, the hybridization of a series of small ring propellanes is studied in order to arrive at a measure of the strain in these compounds     

Palladium-catalyzed addition reaction of polyhaloalkanes to olefins

Pd(OAc)₂ combined with phosphines catalyzes homolytic cleavage of the C—Cl bond of CCl₄ and CCl₃CO₂CH₃ leading to facile addition to olefins under mild conditions. BrCCl₃ also reacts with olefins to give 1,1,1-trichloro-3-bromoalkanes. The reaction is accelerated under CO atmosphere, and the presence of bases such as NaOAc or K₂CO₃ is essential to attain high yields of the adducts.     

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°     

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.     

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.     

Transient ESR nutation signals in excited aromatic triplet states

Transient ESR nutation signals following laser pulse excitation are analyzed for the case of the photoexcited triplet state of acridine in a molecular crystal matrix. Essential features, in particular the short rise-time (< 10^?7) of the signals, can be related to the inhomogeneous nature of the ESR linewidth. Applications are discussed.     

Molecular emission cavity analysis13-a new flame analytical technique : Part II.The determination of selenium and tellurium

The determination of 0.4–4 μg of selenium by molecular emission cavity analysis is described. Selenium in organic compounds is determined after oxygen flask combustion. Metal ion interferences are eliminated by reduction of selenium to the element, filtration onto a glass-fibre paper, and direct incorporation of the filter into the cavity. Applications to the determination of selenium in inorganic and organic compounds are described. The determination of μg-amounts of tellurium is also outlined.     

Partial photoionization cross sections of molecular oxygen

Measurements of partial photoionization cross sections of O₂ for excitation energies between 20 and 45 eV are reported and compared to a calculation using the Stieltjes-Tchebycheff moment theory. Positive evidence is obtained for a predicted σ-type shape resonance between 1 and 2 eV above threshold in certain ionic-state cross sections. Implications for angular distribution of photoelectrons from an oriented O₂ are discussed.     

The Heitler-London interaction energy using the oscillator model

The oscillator model is used to compute the Heitler-London energy and the exchange potential for two interacting hydrogen atoms. With a single oscillator frequency it is not possible to obtain satisfactory results. Allowing the oscillator frequency to vary with internuclear separation enables reasonable values to be obtained.     

Electric field dependence of charge carrier generation in alkane solutions of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)

Studies of the electric field dependence or photocurrents from solutions of TMPD in non-polar solvents are interpreted using Onsager's theory of geminate charge recombination. For all solvents and photon energies, a simple exponential form of the radial distribution function for geminate pairs accounts for the observed field dependence.     

Chemisorption of carbon monoxide on carburized polycrystalline tungsten

Desorption spectra of CO chemisorbed on clean and carburized W at room temperature were measured in the temperature range from 300 to 1900 K and coverage versus exposure plots were constructed. The partial conservation of the β state on carburized W is discussed.     

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.     

Resonant cars spectroscopy of s-tetrazine vapour

CARS experiments on s-tetrazine vapour show that the electronic resonance enhancement in the Q-branch is most effective for the lower J values. This suggests that the radiationless relaxation rate in the excited state increases with rotational quantum number. Delayed picosecond CARS experiments indicate that the rotation-vibration coupling for the 1008 cm^?1 ground-state vibrational mode is approximately 2 MHz.     

Quasiclassical trajectory study of colinear Cl− + HBr → HCl + Br−

Energy distributions in the products of the ion-molecule reaction Cl^? + HBr → HC1 + Br^? have been studied using quasiclassical trajectories on a semi-empirical collinear potential energy surface. Vibrational energy is favored in the products. While some trajectories are long-lived, the kinematic factor of the light central atom prevents effective energy redistribution.     

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%.     

A note on the lower-bound nature of the linearized CPMET

It is shown by a simple demonstration that the energy calculated from the linearized version of the coupled-pair many-electron theory (L-CPMET) of ?í?ek is the same as that would be obtained from the lower-bound equation of the wave operator for pair correlations as derived by Goscinski and Sinano?lu. A possible extension of L-CPMET retaining the lower-bound character is also indicated.     

Mixed ligand complexes of ruthenium(III), rhodium(III) and iridium(III) with dipicolinic acid and some monobasic bidentate nitrogen,oxygen donor ligands

The trivalent ruthenium, rhodium and iridium complexes of dipicolinic acid and its mixed ligand complexes with several nitrogen, oxygen donor molecules, of types: Na[M(dipic)₂]·2H₂O and [M(dipic)(N-O)]·nH₂O (where M = Ru(III), Rh(III) or Ir(III); dipicH₂ = dipicolinic acid; NOH represents different nitrogen, oxygen donor molecules, viz., picolinic acid, nicotinic acid, isonicotinic acid, glycine, aminophenol, o- or p-aminobenzoic acid), have been synthesized and characterised on the basis of elemental analyses, electrical conductance, magnetic susceptibility measurements and spectral (electronic and infrared) data. The parent dipicolinic acid complexes are found to have a six-coordinate pseudooctahedral structure, whereas for mixed ligand complexes, a polymeric six-coordinate structure has been assigned. Various ligand field and nephelauxetic parameters have also been evaluated.     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.