The circular dichroism spectrum of S(+)-sec-butyl benzene

The absorption and CD spectra of S(+)-sec-butyl benzene are reported in the spectral region 195–180 nm. The CD spectrum contains two bands of opposite sign at 190.5 nm and 187 nm. The results are interpreted to confirm previous results for 1-methylindan in this spectral region. The observed bands are assigned to the state derived from the benzene E_2g state.     

Quantum ergodicity and the wigner distribution

A quantum ergodic analysis is developed based on comparison of Wigner phase-space densities of quantum eigenstates to classical densities. The technique is applied to the two-dimensional Henon-Heiles system. Analysis of quantum densities as a function of energy is found to clearly display the regular to ergodic transition.     

A computational approach to the spectrophotometric determination of stability constants-II Application to metalloporphyrin-axial ligand interactions in non-aqueous solvents

The ability of the computer program SQUAD to deduce a plausible equilibrium model, associated stability constants and spectra of individual species is described. The original version of SQUAD has been extensively modified and these changes are detailed. In particular a "user-friendly" method of data input has been implemented that simplifies familiarization with the program. Brevity of program code has been sacrificed in favour of the new data input and error-checking features of SQUAD, with beneficial results. The application of SQUAD to five non-aqueous metalloporphyrin-axial ligand interactions exemplifies the program's ability to handle widely different types of equilibrium systems.     

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.     

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     

Geometry optimization of the ring-opened oxirane diradical: mechanism of the addition reaction of the triplet oxygen atom to olefins

Geometry optimizations of several low-lying diradical states of the ring-opened oxirane (·CH₂CH₂O·) were performed by using the energy gradients of the UHF MINDO/3, STO-3G and 4-31G solutions. Both the STO-3G and 4-3 IG methods predict that the most stable form is the triplet state of the non-twisted σπ conformation in which the unpaired spins localized on the terminal carbon and oxygen atoms are oriented perpendicularly to each other. The singlet σσ diradical state in which both the radical-site p orbitals are coplanar with the molecular framework is only 2.3 (STO-3G) and 1.2 (4-31G) kcal/mol less stable than the triplet σπ diradical state. It is found that the geometry of the singlet σσ diradical is unique in that the C-C-O angle is noticeably small as compared with various other diradical states. Implications of these results to the mechanism of the oxirane-forming O(³P) + C₂H₄ reaction are discussed.     

Exact quantum,quasiclassical forward and reverse reaction probabilities for a colldmear asymmetric model reaction

Detailed quasiclassical and time-independent quantum reaction probabilities are given for a surface on which large discrepancies between quasiclassical and wavepacket results have previously been found. The quasiclassical results are shown to agree relatively reasonably with the oscillation-averaged time-independent quantum ones if the quasiclassical reverse probabilities are chosen in the threshold region.     

Dynamics of three-body half collisions: Ultraviolet and visible photodissociation of s-tetrazine

Ultraviolet (266 nm) and visible (532 nm) photodissociation of collision-free s-tetrazine show asymmetric dynamics with production of one translationally cool and one translationally hot HCN molecule. Furthermore, visible and ultraviolet dynamics are nearly identical, arguing that two-photon excitation is necessary for photodissociation in the visible.     

Experimental study of triplet exciton diffusivity in crystalline pyrene at 300 K

Preliminary measurements of the triplet diffusivity tensor in crystalline pyrene at 300 K are reported. Maximum diffusivity occurs along the b axis and D_ab = (1.25 ± 0.3) × 10^?4 cm² s^?1. Diffusion in the ac′ plane is nearly isotropic with D ≈ (0.3 ± 0.1) × 10^?4 cm² s^?1. These results are tentatively interpreted as diffusion dominated by nonlocal scattering.     

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.