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In the measurement of the photon emission intensity of argon excited by monoenergetic electron impact, as a function of the electron energy, several structures are detected between 24 and 28 eV. They can be attributed to excitation levels of the form 3s3p6nl and to negative ion resonances.

The technique of photoelectron spectroscopy was used to obtain the relative continuum transition probabilities of atomic oxygen at 584 A for transitions from 3P ground state into the 4S, D2, and P2 states of the ion. Transition probability ratios for the D2 and P2 states relative to the S4 state of the ion are 1.57 + or - 0.14 and 0.82 + or - 0.07, respectively. In addition, transitions from excited O2(a 1 Delta g) state into the O2(+)(2 Phi u and 2 Delta g) were observed. The adiabatic ionization potential of O2(+)(2 Delta g) was measured as 18.803 + or - 0.006 eV.

It was aimed to gain information on the nuclear structure of Rb86 by investigation of the 2−→2+ β transition. For this purpose the energy dependence of theβγ angular correlation and the angle dependence of theβγ circular polarization correlation have been measured. A novel experimental set-up has been used for the angular correlation measurement allowing a simultaneous determination of the anisotropy coefficientsA 2 andA 4 under considerable reduction of systematical and statistical errors. For the polarization correlation measurement an unusual experimental arrangement has been applied providing the possibility of simultaneous observation under four different angles. Employing additional data on shape factor measurements and energy dependent circular polarization correlations from other authors the nuclear structure of the 2− state in Rb86 and the 2+ first excited state in Sr86 have been evaluated. For the latter purpose the unified model with weak coupling has been chosen.

Infrared chemiluminescence from vibrationally excited CO was observed when CH3Cl, CH2Cl2, CHCl3, or CH2Br2 was introduced into a stream of oxygen atoms. Emission from vibrationally excited HCl was also observed from CH2Cl2 and CHCl3. The mechanisms describing the reactions of oxygen atoms with these molecules are discussed in detail. The reaction step responsible for the formation of CO† is postulated to be[Formula: see text]and for HCl†[Formula: see text]

The time dependence of electron and ion emission from roughened metals on excitation with a CW CO2 laser has been studied. The emission currents are made up of pulses with durations of several ms. A complex dependence of both ion and electron current on time is observed on time scales ranging from ms to days. An interpretation of these effects based on thermionic emission from localized surface sites is given, and the possible role of exoelectron emission is discussed. Some possible applications of these effects are examined.

We report the first ESR signal of an excited crystalline state (${\ensuremath{\Gamma}}_{6}$) in a metal (PdEr). The intensity of the ${\ensuremath{\Gamma}}_{6}$ isotropic resonance compared to the $\ensuremath{\Gamma}_{8}^{(3)}$ resonances of the ground-state quarter allows the determination of the energy scaling parameter $W$ of the crystalline field. A more precise value is deduced from the splitting of the transitions 1 \ensuremath{\rightarrow} 2 and 3 \ensuremath{\rightarrow} 4 of the $\ensuremath{\Gamma}_{8}^{(3)}$ ground state: $W=\ensuremath{-}0.163\ifmmode\pm\else\textpm\fi{}0.015$ K, in accordance with the work of Praddaude.

It is shown that CNDO S calculations provide 6 significant figures of accuracy in the energies of configurations, and 4 significant figures after configuration interaction. The pairing theorem is shown not to hold in the CNDO S method since all Fμν are calculated and since the Fμμ are not constant. It is further shown that the degeneracies required by the pairing theorem are not even approximated in naphthalene. Finally, using absorption and emission spectroscopic measurements, including triplet-triplet and excited singlet-singlet absorptions, the spectroscopic states of naphthalene are discussed in detail.

The molecular structure of formamide has been redetermined by observing the microwave spectra of the 13 C and 18 O species of NH 2 CHO and ND 2 CHO. The r s structure calculated assuming the planarity of the molecule is NH c = 1.001 6 ± 0.003 A, NH t = 1.001 5 ± 0.003 A, CN = 1.35 2 ± 0.012 A, CO = 1.21 9 ± 0.012 A, CH a = 1.09 8 ± 0.01 A, ∠H c NH t = 121.6° ± 0.3°, ∠H c NC = 118.5° ± 0.5°, ∠H t NC = 120.0° ± 0.5°, ∠NCO = 124.7° ± 0.3°, ∠NCH a = 112.7° ± 2°, and ∠OCH a = 122.5° ± 2°. The strongest satellite of the rotational spectrum is assigned to the first excited state of the amino inversion. The far-infrared spectra observed by King are assigned to the v = 1 ← 0, 2 ← 1, and 3 ← 2 transitions of the inversion, and the v = 1 ← 0 and 2 ← 1 transitions are detected also for the ND 2 CHO species. The observed vibrational frequencies are used to determine the two potential constants V 2 = 156 ± 34 cm −1 /rad 2 and V 4 = 398 ± 29 cm −1 /rad 4 in the potential function to the inversion of the form, V = V 2 τ 2 + V 4 τ 4 where τ is the inversion angle of the amino group. The molecule is thus essentially planar without any potential hump at the planar configuration. The changes of the inertia defect by the excitation of the inversion have been calculated approximately for NH 2 CHO and ND 2 CHO in fair agreement with the observed.

IN small semiclosed seas, tides are excited through their open boundaries by the tides in the more extensive bodies with which they ‘co-oscillate’1–5. Nevertheless the energy dissipated in such seas is not necessarily advected from and lost by, the larger system5.

The effects of internal quantum number consevation are considered in the statistical chain decay of fireballs. A simple model containing I = 1, G = −1, S = 0 mesons (ground state and excited pions) and I = 1 2 , S = 0 baryons (ground state and excited nucleons) is investigated in detail: inclusive distributions, multiplicity distributions and semi-inclusive distributions are determined. The methods are completely general and can be used in more general models with any set of states. As examples, a model with ϱ and π mesons, and nucleons and another one with π and K mesons, and N and Λ baryons are considered.

Consistent analyses are given for the B 3 Π 0 u + -X 1 Σ g + systems of 79Br2 and 81Br2 from separate observations on the absorption spectra of the two isotopes. The emphasis is on 79Br2, where the following levels have been studied: 0 ≤ v ≤ 10 in state X and 0 ≤ v ≤ 55 in state B. For 81Br2, the corresponding levels are 0 ≤ v ≤ 3 in X and 9, 11–13, 16, 19, and 39–54 in B. The extensive data have been used in tests of different methods of determining molecular constants. 1. (i) Rotational constants Bv and Dv for B 3 Π 0 u + of 79Br2 have been determined both by Aslund's term value method and by a constrained band-by-band analysis in which adopted values of B0″, B1″, D0″, D1″ were used. 2. (ii) Constants for both isotopes have been extracted by perturbation theory (up to third order, i.e., to Hv) from RKR potential curves constructed from the constants for 79Br2. Franck-Condon factors and r-centroids for v″ ≤ 10 and v′ ≤ 51 have been calculated for both isotopes from the RKR potentials. The Franck-Condon factors for the v′ = 40 progression of 81Br2 are in good agreement with the relative intensities of the resonance fluorescence series excited in the 40-0 band by the 5145 A line of the Ar+ laser. The density of levels near the dissociation limit of B 3 Π 0 u + has been analyzed according to the Le Roy-Bernstein approximation. The dissociation limits, relative to X 1 Σ g + (v = 0, J = 0) are found to be 19579.76 ± 0.01 and 19581.82 ± 0.02 cm−1 for 79Br2 and 81Br2, respectively. D0 (79Br81Br) for the ground state is then 15895.64 cm−1 or 45.448 kcal mol−1.

It is shown that the improved effective interactions in the fp shell imply the existence of an excited band of states which is much more deformed than the ground state band for some fp shell nuclei. Such states are to a certain extent analogous to the fission isomers occurring in heavy nuclei. Their experimental identification would be interesting and might also help to further improve the effective interaction.

Studies have been made of the photochemistry of cis-dihalogenotetraammineruthenium(III) in aqueous solutions. For the cis-dichlorocomplex, no photochemical reaction has been observed by the irradiation of the visible light region. For cis-dibromo- and cis-diiodo-complexes, a simple aquation of halide ligand seems to occur in a solution with a pH lower than 2.5. The typical values of the quantum yields for the cis-[RuX2(NH3)4] ++H2O\xrightarrowhν cis-[RuX(OH2)(NH3)4]2+X− reaction were 0.27×10−2 (382 nm light) and 0.82×10−2(408 nm light) for dibromo- and dichloro-complexes respectively. The quantum yield was dependent on the wavelength of light, but was independent of the concentrations of halide and hydrogen ions. The quantum yield seems to depend on the oxidizability of the ligand or on probability of the deactivation process in the primary excited state. In accounting for the low quantum yield, it seems most probable that the photoexcited complex species is converted to the ground state by non-radiative ...

Sum rules for matrix elements occurring in calculations of electric quadrupole radiation have been derived and tested for the helium and sodium isoelectronic sequences, using frozencore atomic wavefunctions. Electric quadrupole polarizabilities have been calculated for the metastable 2 1 S and 2 3 S states of He, Li + , Be2 + and B3 + and for the 3 2S states of Na, Mg + and Al2 + . The results serve to confirm the reliability of these wavefunctions for calculating one-electron atomic properties.

The dynamics of collision induced dissociation of I 2 in Xe and Ar was investigated between 300 and 3500 K by means of 3-D classical trajectory technique. For this purpose stratified and importance sampling techniques were adopted to trajectory studies of dissociation. The dissociation cross-sections for I 2 –Ar reaction were computed between 1000 and 3500 K as a function of impact parameter and I 2 internal energy. It was found that for this reaction the overwhelming contribution to the overall rate coefficient comes from trajectories which involve I 2 molecules with initial internal energy ± 1 kT within the dissociation limit. For I 2 –Xe reaction at 300 K the ‘collisional release' mechanism contributes to dissociation and the ‘reactive’ I 2 have a broader energy range between –4 kT to + 1 kT within the dissociation limit. Highly excited metastable I 2 dissociate predominantly by de-excitation collisions in which the total as well as the rotational energy of the reactant molecule is decreased. The equilibrium dissociation rate coefficients (one-way fluxes) for I 2 –Ar system at 1000 and 1500 K, obtained in this work, are consistent with existing experimental rate constants. However, the temperature coefficient of recombination reaction, obtained from shock tube experiments, is more negative than present calculations appear to suggest.

The approximate equation I e = 2 I 8 - I 0 , where I e , I 8 , and I 0 are, respectively, the equilibrium, substitution and zero-point moments of inertia of a molecule, can be derived from a first order treatment of isotope effects, and is valid for linear, symmetric or asymmetric tops. By means of this equation it is possible to estimate the equilibrium structure of a molecule from the zero-point rotational constants of several isotopes. The advantage of this “mass-dependence” ( r m ) method over the conventional r e method is that it is insensitive to the perturbations and resonances that frequently affect excited vibrational states. The main disadvantages are that a large number of isotopic molecules may be necessary and that the above equation is not sufficiently accurate for hydrogen-deuterium isotope effects. A detailed comparison between r m and r e of CO shows that the slight difference of about 2 × 10 −4 A between the two bond lengths is due mainly to the difference in the contributions of the electrons. The r m method has also been applied to the triatomic molecules N 2 O, OCS, SO 2 and HCN. For N 2 O and SO 2 the results are in excellent agreement with the most recent r e structures. For OCS there is a significant difference between the r m structure and the present r e structure. This difference is as yet unexplained. The poor results for HCN confirm the general expectation that the r m method cannot be applied to hydrides without further modification.

The positive parity particle-hole states in 16O were investigated in various TDA and RPA calculations. Their decay strength to ground was evaluated for general operators acting in orbital, spin and isospin space in order to search for possible collective effects. Some evidence was obtained for a weak collectivity for the hexadecapole state and some of the spin-multipole states, particularly in the case J = 2, T = 0, if a harmonic oscillator basis is used.

Kinetic rate parameters can be determined from recoil tritium reaction studies although the energy distribution of the reacting tritium atoms is not known. T is produced by /sup 3/He(n,p)T. Recoil T-for-H substitution on cyclohexene gives excited cyclohexene-t molecules. The dependence of product yield on pressure (in the hexene-t molecules decomposed unimolecularly to give ethylene-t and butadiene-t with an apparent rate constant (at 135 deg ) of 5 x 10/ sup 6/ s/sup -1/. The s parameter in the RRK (Rice, Ramsperger, and Kassel) treatment of the unimolecular decomposition of cyclohexene was determined as s = 24. Similarly, the pressure dependence of product yield showed that cyclohexyl-t radicals which are fornaed by recoil T atom addition to cyclohexene decomposed unimolecularly to give n-hexene-t, 1-butene-t, and methane-t with rate constant 8 x 10/sup 3/, 3 x 10/sup 4/, and 5 x 10/sup 2/ s/sup -1/, respectively . The relative nate of abstraction vs addition of radicals in alkenes was determined from the scavenger dependence of the yields of products with a nadical precursor. (40 references) (auth)

Equations are derived for the currents in the load of a two-wire transmission line illuminated by the nonuniform fields of a small coplanar loop. Since the derived equations contain complicated integrals requiring machine computation, an approximate solution, which is applicable to most coupling geometries and which greatly reduces the computational effort, is also developed. In a numerical example, the currents excited by the loop are compared with the currents excited by a plane wave.

A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method.

The vertex operators associated with the transverse states of DRM are explicitly written. As an application of this result the couplings of three excited «transverse» states are explicitly computed.

The resonance Raman spectra of β-carotene in isopentane solution have been obtained at low temperature, using eight output lines of the argon-ion laser and a line of the heliumcadmium laser. The excitation profiles of three fundamentals, two overtones, and two combination tones are presented and analyzed in terms of the Albrecht theory. The overlap integrals between the vibrational wavefunctions of the ground and first excited electronic states are shown to be the most important factor for the resonance Raman intensities of the β-carotene molecule. The observed excitation profiles and absorption spectrum at low temperature have been successfully simulated by assuming small displacements of the equilibrium nuclear positions in going from the ground electronic state to the first excited. Elongation of CC bonds and shrinkage of CC bonds in the excited electronic state have also been estimated.

A photoionization mass spectrometer has been used to study the reaction of ground-state oxygen atoms with acetylene. The oxygen atoms were produced in the absence of molecular oxygen in a discharge-flow system with nitrogen as the principal carrier gas. Several of the free radicals and stable product molecules that were observed previously have been studied in more detail. Experiments with added gases have shown that the methylene radicals observed are probably in their ground, triplet state. The ratio of rate constants for the reactions of CH 2 with O 2 and O respectively was found to be approximately 1:10. The dependence of the C 3 H 3 radical concentration on the experimental conditions showed that C 3 H 3 was formed in a secondary reaction, probably involving an excited molecule or radical. The rate constant for the reaction of the HCCO radical with O 2 was measured as 2.2 ± 1.2х10 7 1 mol -1 s -1 . The product observed at mass 42 appears to be ground-state ketene formed in the primary step, perhaps via a triplet state. However, the possibility that the ketene might be formed in a secondary process cannot be dismissed. The rate constant for the reaction of ground-state oxygen atoms with ketene was measured, with a result significantly lower than a previous study. The diacetylene concentration showed a complex dependence on reaction conditions. Analysis of the approach of [C 4 H 2 ] to its steady-state concentration gave a rate constant for the reaction of oxygen atoms with diacetylene of 1.6 ± 0.5 х10 9 1 mol -1 s -1 . The relation of these results to previous studies is discussed briefly. It is suggested that a reaction of one or more of the energetic primary products, such as electronically excited CH 2 , HCCO or ketene, could be responsible for the chemiluminescence of CH, OH and CHO.

The paramagnetic resonance spectra of the ground 2P3/2 and excited 2P1/2 levels of both isotopes, 35Cl and 37Cl, of atomic chlorine have been observed. The off-diagonal magnetic dipole coupling constant A3/2, 1/2 and the metastable state g factor gj(2P1/2) have been evaluated from measurements on selected transitions to an accuracy of about two parts per million in the transition frequency. The magnetic dipole radial parameters [Formula: see text], [Formula: see text], and [Formula: see text] for chlorine are calculated.

The Hartree-Fock (HF) minima for the nucleus28Si were obtained for the prolate, oblate and spherical shapes using the interaction obtained by Preedom and Wildenthal. The interaction gives rise to large energy separation between the prolate and the oblate shapes. The spherical solution is just 2 MeV above the lowest HF (oblate) minimum. The spectrum projected from the oblate HF state is in good agreement with the experimental spectrum. The transition probabilities for the different energy levels also agree reasonably well. The configuration mixing calculations performed on the basis of states projected from the three shapes indicate that there is no significant mixing of different projected states. The second 0 2 + state, thus obtained, corresponds to the third 0 3 + state in the experimental spectrum and stems dominantly from the spherical HF state. It is seen that the structure of the energy levels of28Si, especially the second 0 2 + level is very sensitive to the two body interaction. The results are compared with those obtained using the renormalised interaction of Kuo.

The microwave spectrum of chloromethyl methyl ether has been studied in the region 12.4–40 GHz. For 35Cl species, a- and c-type transitions have been assigned for the ground state, the first excited state of the chloromethyl torsional mode, and the first excited state of the methyl torsional mode. Assignments were also made for the ground state of 37Cl species. The assigned transitions are due to the gauche conformer. The nuclear quadrupole coupling constants were determined for the ground state of 35Cl and 37Cl species. The observed A-E splittings of the rotational transitions arising from the three vibrational states indicate a strong coupling between the two torsional vibrations. A model calculation based on the Hamiltonian previously used by Butcher and Wilson (J. Chem. Phys. 40, 1671 (1964)), was carried out to account for the splittings and the vibrational frequencies of the two torsional modes. The barrier to internal rotation of the methyl group is estimated to be V3 = 647 ± 17 cm−1 (1.84 ± 0.05 kcal/mole).

New sharp bands of formic acid have been observed in the near ultraviolet at the long wave-length end of the previously observed diffuse band system (2250–2500 A) by considerably extending the absorption path length. Both the diffuse and sharp bands belong to the same vibrational system which is assigned to the π ∗ ← n electronic transition in the carbonyl group. Extensive progressions are observed in the carbonyl stretching frequency which is greatly reduced in the excited state (fundamental ν3′ ≈ 1080 cm−1) and many intervals of about 400 cm−1 are assigned to the OCO bending frequency ν7′. A band contour analysis of the 2593 A band shows that the molecule is nonplanar in the excited state because of the magnitude and sign of the inertial defect. From this analysis, the rotational constants for the excited state are S ‘ =1.8755, B ‘ 0.4042, C ‘ =0.3378 cm −1 By the plausible assumption that the important changes in the molecule are in the C=0 bond length, the OCO angle, and the nonplanarity due to the formyl hydrogen, the following excited state parameters are derived.rC=0 = 1.407A.The changes in formic acid are closely analogous to the changes in formyl fluoride as a result of the π ∗ ← n transition.

The rotational line intensity, partial band intensity and peak band intensity methods (the latter used in conjunction with computer-generated synthetic spectra) have been used to interpret photoelectric and photographic measurements on the astrophysically important C2Swan band system, stably excited in a direct current discharge through C2CI6+ A. All measurements lead to a consistent (within 5% ) expression for the variation of the electronic transition moment with internuclear separation ofRe(r)=C(1.00-0.25r) 1.120

The microwave spectrum of CH3SS CD3 was investigated in the range of 5 -40 GHz. Rotational spectra in different states of the S-S-torsion were assigned. The methyl torsion fine structure of these spectra was measured and compared with calculations based on a Hamiltonian formulated for a model with two internal degrees of freedom, the methyl and S-S-torsion.

The problem of the threshold law for electron-atom impact ionization is reconsidered as an extrapolation of inelastic cross sections through the ionization threshold. The cross sections are evaluated from a distorted wave matrix element, the final state of which describes the scattering from the Nth excited state of the target atom. The actual calculation is carried for the e-H system, and a model is introduced which is shown to preserve the essential properties of the problem while at the same time reducing the dimensionability of the Schrodinger equation. Nevertheless, the scattering equation is still very complex. It is dominated by the optical potential which is expanded in terms of eigen-spectrum of QHQ. It is shown by actual calculation that the lower eigenvalues of this spectrum descend below the relevant inelastic thresholds; it follows rigorously that the optical potential contains repulsive terms. Analytical solutions of the final state wave function are obtained with several approximations of the optical potential.

The triple headed and violet degraded band of SiO at 2970 Å has been excited in a high frequency discharge through a mixture of SiCl4, oxygen, and argon flowing at low pressures. From a study of the high resolution spectrum, this band has been assigned to a 3Σ–3Π transition. The final state has been identified with the well known a3Πr state of SiO, and the initial state has been designated as the d3Σ and located at 33 640 cm−1 above the a3Πr. The rotational constants determined for the d3Σ state are (in cm−1): [Formula: see text]

The lower n,π* and π,π* excited state energies of four tomj-polyenecarbaldehydes, acrolein, 2,4-pentadienal, 2,4,6-heptatrienal, and 2,4,6,8-nonatetraenal, were calculated within the framework of the conventional P-P-P SGF-MO-CI method and then discussed. Also, the oscillator strength for the π,π* transition was obtained in terms of the dipole length and the dipole velocity.

Cross sections have been measured for the disorientation of the 3 1D, 4 1D, and 5 1D states of 3He in collisions with the ground state atoms. Oriented n1D state atoms are produced by exciting in a discharge 3He atoms whose nuclei have been oriented by optical pumping. The role of hyperfine coupling is investigated and the theoretical treatment of the effect of collisions on the orientation of the excited atom, which does not require instantaneous recoupling of the nuclear spin I and the electronic angular momentum J after each collision, is presented.

The half-life of the 379.3 keV state of 169Tm has been reinvestigated by the delayed coincidence technique. The result, T1/2 = 49.8 ± 1.5 ns is about 40% larger than the result by Berlovich et al. which had been generally accepted in the literature.

Band contour analyses of the absorption bands of 78Se16O2 and 80Se16O2 at 2949 A, assigned to the 103 transition (King and McLean, in press), show that they are type A, with transition moment directed in-plane and parallel to the line joining the oxygen nuclei. The electronic transition responsible for the B absorption system of the molecule is therefore 1 B 2 - X 1 A 1 under the C2v point group. The contour analysis gives the excited state bond angle as 101.0°, and the bond length as 1.74 A. The latter value is confirmed by Franck-Condon calculations. There is therefore an increase in bond length and a decrease in bond angle upon electronic excitation. This agrees with the predictions of molecular orbital theory.

In the course of our studies of the chemiluminescence of xanthene dyes, we found the violet chemiluminescence emission (CL-emission) resulting from the reaction of succinylfluorescein with oxygen in an aerated alkaline aqueous system of a high concentration of an aprotic solvent (DMSO or DMF), an especially intense emission occurring in aerated dry DMSO or DMF with tert-BuOK as base. The CL-emission comprised two emission components: an intense violet emission (a peak, at 410 nm) whose spectral distribution was similar to that of the fluorescence band which appeared during the course of the reaction, and a weak greenish-yellow emission similar to the fluorescence of the dye. By isolating and identifying the violet-fluorescent reaction product with an authentic sample, and by comparing the CL-emission with the fluorescence emission of the isolated product, it was concluded that the violet CL-emission may be attributed to the formation of an excited dianion of 3,6-dihydroxyxanthone. The reaction path leadin...

A magnetoplasma with isotropic distribution of particle velocities is unstable against the electron cyclotron modes, excited by the presence of a population of suprathermal electrons. The nonlinear interaction of these waves with resonant suprathermal electrons, whose initial velocity distribution was isotropic, causes diffusion in the velocity space. The distribution of suprathermal electrons becomes anisotropic. This may under certain conditions lead to new instabilities driven by the anisotropy in the velocity space. The temporal evolution of the 'plateau' and the characteristic relaxation time of the quasilinear interaction has been analyzed.

The quadrupole moments of the first excited states and the reduced transition probabilities for E2 transitions in even-even Ti, Cr, Fe and Ni isotopes are calculated from the projected Hartree-Fock-Bogolubov wave functions in the 2p-1f shell. The overall agreement between the calculated and experimental results is quite good.

Rotational assignments in the ν6 + ν9 type-A band and the ν9, ν6 + ν11, and ν1 + ν6 type-B bands of ethylene-1,1-D2, recorded at a resolution of ∼0.03 cm−1, enable the ground state rotational constants to be determined much more accurately than previously. A significant change in the A0 constant is noted. All upper states suffer perturbations to their rotational structures. Analyses, excluding the areas of perturbation, still enable the excited state constants to be determined with considerable precision.

The absorption and fluorescence spectra of pyrazine have been observed in vapor, solution and crystal, and the vibrational structures have been analyzed in detail. The fluorescence spectrum consists of long progressions of the nontotally symmetric vibration ν5(b2g), and the absorption spectrum contains also the progression of the corresponding excited state vibration ν′5(b2g. However, the pattern of the latter progression is unusual because of the highly anharmonic nature of the potential of the 1B3u state, which may be expressed by a functional form containing a quadratic term in the normal coordinate. All the experimental results suggest that the known vibronic interaction between the 1 B 3u (n,π ∗ ) state and the 1 B 1u (π, π ∗ ) state through the vibration ν2(b2g) is strong. The vibronic coupling and the potential of the 1B3u state were found to be very sensitive to solvent.

By considering the anisotropy of the decay distributions of excited clusters, or equivalently their spins, in the diffractive excitation model, we show how the forward peak of the differential cross section for excitation is broadened. Furthermore, it is shown through unitarity how the elastic peak is sharpened. An algebraic relation between the slopes is derived. In a self-consistent model, the excitation slope for large cluster masses is half the elastic slope.

A technique for measuring the decay of localized excited triplet states into the delocalized band states of a solid utilizing the optical detection of electron spin coherence is described. Specifically, the use of optically detected electron spin locking for measuring kinetic phenomena in the presence of fluctuating triplet spin sublevel populations is presented and illustrated. In addition, preliminary experimental data is reported which yields the temperature dependence of the phonon assisted promotion of a localized isotopic site to an energy equal to that associated with the energies of the host exciton band. Finally, the data is analyzed in terms of a kinetic model which relates the localized state's rate of promotion and radiationless decay into the exciton band states to explicit features of the exciton and phonon band structure.

The Stark effect on the rotational lines of the 0–0 band of the [Formula: see text] system of propynal has been studied with field strengths up to 20 kV/cm. Measurements of the Stark shifts and splittings for the qQQ2(7,7), qQQ2(8,8), and qQQ2(9,9) lines in parallel polarization lead to a value of µa′ = 0.5 ± 0.1 D for the dipole moment of propynal in the ã3A″ excited state.

High-resolution measurements of the α-particle transfer reaction 40 Ca( 16 O, 12 C) 44 Ti have been performed utilizing a split-pole magnetic spectrograph. Comparison with 40 Ca( 6 Li,d) 44 Ti data reveals close agreement for the relative selectivity of final states in the two transfer reactions. No evidence is found for α-particle breakup of 16 O or population of the 4.43 MeV first excited state of 12 C.

A model is presented which relates the dynamics of energy migration in crystals to the mechanism by which thermal equilibrium between delocalized band states and localized trap states is achieved. Central to this model is the requirement that coherent energy migration must be the dominant mode of migration at low temperatures in order to achieve Boltzmann equilibrium between band and trap states within the lifetime of the excited electronic state. Second, a stochastic model for detrapping is developed which is based on an irreversible radiationless relaxation process of a phonon-trap intermediate into the density of delocalized band states. Explicit account is taken of phonon-trap interactions in the formation of the excited trap intermediate. Further, the relation between detrapping and the ability of a crystal to achieve thermal equilibrium within the excited-state lifetime is developed and applied to one-dimensional crystals. Experimental results on molecular crystals representing examples of one-dimensional exciton bands are also presented. Specifically, the temperature dependence of phosphorescence from excited triplet trap states is interpreted in terms of the above considerations. From these experiments one can obtain both the sign of the intermolecular interaction and the dispersion of the first excited triplet band in addition to an estimate of the coherence length associated with exciton migration in the Frenkel limit. Finally, some new and unique methods for studying energy migration are presented which utilize optically detected magnetic-resonance techniques in zero field. They include experiments based on the measurement of electron-spin coherence in the rotating frame and the relationship of the spin coherence to the various rate processes important in trap-exciton interactions.

The principal purpose of the present paper is to develop a formal, rigorous theory of Frenkel excitons with or without interaction with an external electro-magnetic field within the framework of a two-level-atom model. Employed implicitly but extensively in exciton problems have been model systems composed of interacting two-level atoms in which only two of energy levels of a given atom, corresponding to the ground state and an excited state, endowed with a transition dipole moment, are taken into account. The most common method traditionally employed here is to treat Frenkel as well as Wannier excitons simply as Bosons. It is however to be reminded that excitons, both Frenkel and Wannier types, are neither Bosons nor Fermions. Specifically, Frenkel excitons in such a model system are to be considered as Paulions or being equivalent to S=1/2 spins. Except for the specific case of one-dimensional system with nearest-neighbour interactions only,1) the conventional procedure, in analogy with magnons in Heisenberg magnets, would be to regard excitons as a non-ideal Bose gas in which the deviation from the Bose statistics is expressed in the form of effective interactions among excitons, called kinematical interactions.2),3) The discussion along this line however is generally much involved. Furthermore, there exist intrinsic or dynamical exciton-exciton interactions, even if they are regarded as Paulions or, more generally, as electron-hole pairs. It is shown in this paper that within the framework of a two-level-atom model the model exciton Hamiltonian is rigorously expressed in the form of the Heisenberg model Hamiltonian for S=1/2 spins with long-range anisotropic exchange interactions, and that Frenkel excitons thus obtained are generally expressed as quantum-mechanical nonlinear polarization waves, the nonlinearity being characterized by the atomic level population.