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%.     

Resonance Raman scattering near a threshold for dissociation

The threshold behavior of Raman amplitudes for photon energies near dissociation of the intermediate potential surface of a diatomic molecule is determined. Structure in the Raman amplitudes is calculated and found to be due to resonance of the intermediate potential surface.     

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.     

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 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.     

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.     

Thermal properties of xenon adsorbed on graphite

We report theoretical results for dynamical and thermodynamic properties of the bare graphite (0001) surface, and with a physisorbed monolayer of xenon. The surface vibrations of graphite are less pronounced than those in more isotropic crystals. The surface-excess specific heat of the bare surface peaks at 45 K, that of the xenon at 13.5 K.     

Analysis of tellurides of lead and tin by automatic titrations

An analytical method based on automatic potentiometric EDTA and redox titrations was developed for the analysis of tellurides of lead and tin.First, the sum of lead and tin is titrated at pH 4.5 by adding a known excess of EDTA and back-titrating with a standard lead solution. After addition of ammonium fluoride to mask the tin, the EDTA released from the Sn-EDTA complex is titrated with standard lead solution. Alternatively, after the determination of total lead and tin, lead may be determined by back-titration with standard lead on a separate sample aliquot using tartaric acid to mask the tin. Tellurium is separated as tellurous acid, which is then dissolved in a dilute sulfuric acid solution and oxidized by permanganate at room temperature; the excess permanganate is back-titrated with iron(II) solution automatically. This titration may also be used to determine tellurium in the presence of lead and tin after treatment with perchloric acid. Accuracies of 0.1-0.2% can be obtained.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

Assignment of photoelectro bands for naphthalene and anthracene by penning ionization electron spectroscopy

The Ne¹(³P₂) Penning electron spectra and the Ne I photoelectron spectra were measured in the gas phase. The observed systematic differences in their relative intensities were interpreted in terms of the electron distributions of the relevant molecular orbitals and used for assignment of the deep π bands, π₁ (12.4 eV) for naphthalene, and π₂ (11.9 eV) and π₁ (12.8 eV) for anthracene.     

Vibrational lineshapes of adsorbates: the role of substrate electronic excitations

The vibrational spectrum of an atom or molecule adsorbed on a metallic surface is influenced by the dynamic interaction between the localized oscillator and the continuum of electron-hole pair excitations in the solid. Features of an exactly soluble model for this interacting system are presented, the local spectral function is obtained in terms of calculable level shift and broadening functions, and some prototypical numerical results are displayed and discussed.     

Interference effects in the predissociation of H2 and HD

Several absorption lines in the B? ¹Σ⁺_u ← X ¹Σ⁺_g system at 83 nm have been observed with sub-Doppler resolution in H₂ and HD. A detailed analysis of the lineshapes arising from the homogeneously predissociaied B ¹Σ⁺_u states shows that the linewidths are strongly affected by the Franck-Condon factors associated with coupling to the B' ¹Σ⁺_u continuum.     

CNDO/2 molecular orbital calculations on the conformational modes of γ-aminobutyric acid

γ-aminobutyric acid and its zwitterion have been studied using the CNDO/2 method. The predicted minimum energy conformations, dipole moments and net atomic populations are reported. The effects of the polarity of the GABA zwitterion on its preferred conformation are discussed.     

Two-photon laser-induced fluorescence in oxygen and nitrogen atoms

Two-photon absorption is used to populate the 3p ³P state of O and the 2s²2p²3p⁴D^o state of N in a flow discharge. Exciting photons are produced by anti-Stokes Raman frequency conversion of tunable UV laser radiation; the resulting near IR fluorescence from the excited state yielded lifetimes, quenching rates, and relative two-photon transition probabilities.     

Cationic di- and mono-carbonyl complexes of manganese(I)

The complexes fac-O₃ClOMn(CO)₃(NN) (NN = 1,10-phenantroline (phen) or 2,2'bipyridine (bipy)) react with an excess of the ligands L [L = P(OR)₃ or P(OR)₂Ph, R = Me or Et] in refluxing ethanol to give cis-trans-[Mn(CO)₂-(NN)L₂]ClO₄, or the more highly substituted [Mn(CO)(NN)L₃]ClO₄ if the reaction is carried out under UV irradiation. Carbonylation at normal pressure of the latter complexes results in the formation of cis-cis-[Mn(CO)₂(NN)L₂]ClO₄, which undergo isomerization to the cis-trans isomer when heated in acetone.Treatment of fac-O₃ClOMn(CO)₃(dpe) (dpe = 1,2-bis(diphenylphosphino)-ethane] with bipy or phen in refluxing ethanol gives the corresponding cis-[Mn(CO)₂(NN)(dpe)]ClO₄ complexes, and irradiation of these with UV in the presence of an excess of P(OR)₃ (R = Ph, Et or Me) gives the monocarbonyls [Mn(CO)(NN)(dpe)L]ClO₄.     

Energy transfer rates for vibrationally excited gas-phase azulene in the electronic ground state

Gas-phase azulene molecules were prepared with 17200 cm^?1 vibrational energy in the S₀ state by laser excitation of the S₁ state and subsequent internal conversion. Rates of vibrational energy removal (for several collision partners) were determined from the decay of the CH-stretch fluorescence at 3.3 μm. A stepladder model indicates each azulene-azulene collision removes 3500 cm^?1 of vibrational energy.     

Vibrattonal excitation of molecules by collisions with “hot” hydrogen atoms from laser photolysis

Excimer laser (ArF) photolysis of diatomic and triatomic hydrides produces hydrogen atoms with translational energies in excess of 15000 cm^?1 per atom. Subsequent collisions of these “hot” atoms with CO₂ and N₂O produces vibrationally excited molecules which can be detected by their characteristic infrared emission.     

Intersystem crossing rates of pentacene in naphthalene at 1.9 K following single-mode laser excitation

The rates of nonradiativ decay and the spectra of pentacene in naphthalene are reported. The experiments were carried out at 1.9 K using a single-mode dye laser. The results in the naphthalene host are consistent with our earlier observation of transients in the p-terphenyl host, and suggest a slow rate for intersystem crossing in the molecule.     

An empirical potential for the O-H ⋯ O hydrogen bond: Part 2. Comparison with observed hydrogen bond geometries

The room temperature distribution of O-H ? O hydrogen bond geometries has been predicted by a Monte Carlo calculation, with an empirical potential energy function for the hydrogen bond. The results are compared with a recent survey of hydrogen bonds in carbohydrate crystal structures. The calculated and observed distributions of the O-H ? O angle have mean values of 165.5° and 167.1° respectively. Both the theoretical and experimental results suggest that short O ? H hydrogen bonds tend to be more linear than long O ? H bonds. The distribution of hydrogen bonding within the lone pair plane of the acceptor oxygen atom is predicted to be broader than the distribution perpendicular to this plane, in agreement with the experimental data. The empirical hydrogen bond function, in conjunction with the molecular mechanics program MMI, has also been used to predict the geometries of inter-residue hydrogen bonds in five disaccharides. The O ? H distances and O-H ? O angles are reproduced with r.m.s. deviations of 0.06 Å and 9° respectively.