The absorption spectrum of carbonyl selenide: Rydberg transitions

The vacuum ultraviolet spectra of the isotopic species OC⁷⁸Se and OC⁸⁰Se have been measured under both low and high resolution down to 1200 Å. Twelve distinct absorption systems have been vibrationally analyzed, and estimates obtained for excited-state geometries in some cases. Observed transitions have been assigned as members of nsσ, npσ, npπ, and nd Rydberg series, and the quantum defects determined. As n increases, the tendency to ($\text{Ω}$, ω)-type coupling also increases.     

A study of relative level populations in beam-foil excited Li,Be, and Mg

We have studied the optical beam-foil spectra of Li, Be, and Mg in the wavelength region 200–550 nm by use of a quantum efficiency calibrated monochromator at projectile energies of 210 keV for Li, 156, 256, and 356 keV for Be, and 100 keV for Mg. The relative population for different Rydberg levels of the same term series decreases in most cases somewhat faster than (n ^*)^?3, as is also observed in ion-atom encounters under single collision conditions. The relative level population for levels of the same principal quantum number increases generally with the orbital angular momentum quantum number, and superimposed on this increase is a peaking forp levels. The relative population of levels of the same charge state and with the same core configuration is unaffected by change of the projectile energy.     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

Investigation of the double diffraction dissociation reaction pp → (pπ+π−) (pπ+π−) at 24 GeV/c

Data from a high-statistics bubble chamber experiment at 24 GeV/c are used to study the double diffraction dissociation reaction pp→(pπ⁺π^?) (pπ⁺π^?) where both protons of the initial state dissociate into pπ⁺π^? systems. Cross section, mass spectra and dσ/dt' distributions have been determined and are compared with the results found for the single diffraction dissociation reaction pp → p(pπ⁺π^?), which have been obtained from the same experiment. All our findings agree well with what is expected from the factorization hypothesis.     

Rydberg states of carbon dioxide and carbon disulfide

The electronic absorption spectra of carbon dioxide and carbon disulfide have been reexamined. Model potential calculations have been used to calculate the energies of excited states in Rydberg approximation, and (npσ) and (npπ) Rydberg series have been assigned. For both molecules, the lowest excited ¹Π_g and ¹Π_u states are identified as Rydberg states. The lowest ${}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ state is mainly Rydberg for CO₂, but contains some valence character for CS₂, There is no evidence for transitions to additional valence states of these symmetries.It is shown that $\text{LCAO}\text{MO}$ predictions about excited states can be misleading because of near-linear dependencies which arise in multicenter expansions. A consideration of the united atom orbitals for CO₂ and CS₂ predicts that there should be only the number of low-energy excited states which are found from the spectral analysis.     

New valence and Rydberg states of the P18O molecule

The absorption spectrum of the P¹⁸O molecule has been studied in the region 1650–1800 Å. The upper levels of the transitions are shown to be levels of new ²Π valence, ²Π Rydberg and ²Δ Rydberg states of the PO molecule. Most of the levels are perturbed; some of them are predissociated. The new valence state P²Π corresponds to a regular state of the electronic configuration $\text{σ}{}^2\text{π}{}^3\text{π}{}^{12}$ and the ²Π and ²Δ Rydberg states belong to the 5p, 3d, 4d complex series. Perturbations of the P²Π state are shown to arise from Rydberg ～ Non Rydberg interactions with states of same or different symmetry. The complexity of the interactions does not allow to carry out a deperturbation but a comparison with the data of the P¹⁶O molecule allows to give a vibrational assignment to the levels of the P²Π state.     

Vibronic structure of the 3s Rydberg state of the 2-methylallyl radical

Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled 2-methylallyl (C₄H₇) radicals provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following one-photon and two-photon excitation of rovibronically cold 2-methylallyl radicals and its isotopologues C₄H₄D₃ and C₄D₇ reveals transitions to more than 30 vibrational levels in the 3s Rydberg state that are identified and reassigned on the basis of predictions from ab initio calculations and results from pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained with resonant multiphoton excitation via selected intermediate states. Depletion spectroscopy reveals transitions to short-lived 3p Rydberg states that have a large oscillator strength.     

Scaling of semi-inclusive cross sections with respect to longitudinal and transverse momenta

The semi-inclusive one-particle transverse and longitudinal momenta spectra of π^± mesons have been studied in the centre-of-mass system for π^?p interactions at 40 GeV/c. These data are compared with similar data from pp interactions at 300 GeV/c and lower energies. Distributions in the variables p_T/〈p_T〉 and p_L/〈p_L〉 reveal scaling properties, which are found to be substantially independent of the nature of the projectile, of the incident energy and of the prong multiplicity. These spectra are reasonably described by universal functions.     

Pi-mesic decays of A = 4 hypernuclei

Angular distributions and energy spectra for the decay modes _Λ⁴He→π^?p³He, _Λ⁴H → π^?p³H, _Λ⁴H → π^?n³He are calculated and compared with experiment. Final state nuclear interactions have been adjusted to fit the corresponding scattering data. With S-, P- and D-wave interactions we were able to obtain reasonably good agreement with the experimental decay spectra. It is suggested that the _Λ⁴H → π^?n³He decay spectra may be decisive in selecting the right set of p³H complex phase shifts from several possible solutions.     

Absorption spectrum of naphthalene in rare-gas matrices

The absorption spectrum of naphthalene has been studied in rare-gas matrices (RGM). Molar extinction coefficients have been determined and oscillator strengths of various $\text{π}{}^1\text{-π}$ transitions deduced. Bands in the 6.5 to 7.1 eV region, some of which were previously observed and interpreted as members of an impurity exciton (Rydberg) series, have been assigned to a $\text{π}{}^1\text{-π}$ transition. The results are compared with the theoretical prediction.     

Investigation of the 6p 2(3 P 0)n p Rydberg series of bismuth by multiphoton excitation

Rydberg states of the odd-parity series 6p ²(³ p ₀)n p of BiI are excited by a three-photon process. A two-photon dissociation of Bi₂ into excited atomic states followed by a one-photon absorption leads to highly excited atomic Rydberg states up ton = 32. States of the even-parity Rydberg series 6p ²(³ p ₀)nsJ=1/2,ndJ=3/2 andndJ=5/2 are also observed. In order to avoid the background caused by ionization of the bismuth molecules we performed a two-color excitation with pulsed dye lasers. With this experiment the 6p ²(³ p ₀)npJ=3/2 Rydberg series could be resolved up ton=75. The increasing quantum defect of this series is due to a perturbing state close to the first ionization limit. By a MQDT analysis we obtain the energy of the perturbing state and a value of 58,761.68±0.1 cm^?1 for the first ionization limit of atomic bismuth.     

Interpretation of rare-gas-induced broadening of Rydberg series lines

Approximate expressions have been derived for the cross-sections of rare-gas-induced broadening of the Rydberg series lines on the basis of the interatomic potential which is expressed as a combination of the van der Waals potential, the Fermi potential and the polarization potential. Only the effect of elastic scattering has been taken into account. Multichannel (two-channel) quantum defect theory has been combined with the broadening theory to include the effect of the mutual interaction of the Rydberg series. The resulting cross-sections are in reasonable agreement with the experimental values obtained for Na by Kachru et al. and for Ca and Ba by Ueda et al.     

Observation of neutron-neutron interactions with double diffraction dissociation at the ISR

Neutron-neutron interactions have been observed at the CERN ISR with deutron colliding beams. The double - diffraction dissociation process →(pπp^?)(pπ^?) has been measured with the Split Field Magnet at √s = 26 GeV detecting all final state particles, including the two spectator protons. Mass and t distributions are presented and compared with corresponding spectra observed in single neutron diffraction in the same energy range with supporting evidence for factorization. The cross-section of the process is 11.5±2.8 μb and can be directly related to the corresponding value for double diffraction dissociation of protons in the same energy range.     

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

2?+?1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0–10.5?eV have been observed. The excited vibronic symmetry has been determined from polarization-ratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to π*?←?π, 3p?←?π, 4s?←?π, 4p?←?π, and 4d?←?π transitions. Vibrational progressions related to the CH₂ twisting (ν₄ ～770?cm^?1) have been observed for several excited electronic states. Calculated Franck–Condon factors also confirm that CH₂ twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.     

Fractal diffusion processes in particle physics

A series of consistent measurements of kinematic variables for pion diffraction production processes by pions with an initial momentum of about 4 GeV/c were analyzed: π ⁺ + p → p + 2π ⁺ + π ^? and π ^? + p → p + 2π ^? + π ⁺. The Hurst method analysis discovered the presence of the memory effect for both data arrays. The distributions of the transition probability density appeared to seek some equilibrium shape, characteristic of the fractal Brownian motion (FBM). The process can be defined by the special diffusion Fokker-Planck equation (FPE). The obtained values of Hurst coefficient 0.5 < H < 1, which is a parameter of FPE, mean that the processes explored are realized in fractal generalized phase space with fractional dimension.     

Relative intensities in X-ray photoelectron spectra.: Part VIII

The photoionization cross-sections for the 3s and 3p shells of atomic Si, P, S, and Cl and the S²⁺ ion, and for the 2s and 2p shells of atomic F have been calculated using the random-phase approximation with exchange (RPAE) for the average-configuration term. Using the theoretical atomic cross-section values, the partial cross-sections for photoionization of the SF₆ molecule have been calculated for hv ? 54 eV and the photoelectron spectra have been interpreted. The calculation of relative intensities in the photoelectron spectra of H₂S is presented. The influence of the effective charge of an atom on the photoionization cross-section value for a molecular level is shown.     

Efficient field-free orientation of CO molecules using a three-step excitation scheme

We report results from detailed state selective photo-recombination study along with the doubly excited autoionizing resonances in Be-like C²⁺ and Al⁹⁺ ions. In the present investigation, the primary focus is on detailed energy profiles of the individual photo-recombination cross sections. The calculation was carried out for the excited Rydberg states of type 1s ²2sns(¹S^e) which interact with the odd-parity continua up to the C³⁺ and Al¹⁰⁺ 2p threshold limit. The numerical evaluation has been performed at a fine energy mesh across all the autoionizing Rydberg series of resonances 1s ²2pns(¹P⁰) converging to Li-like ion 2p threshold. The method of calculation keeps the essential ingredients of the Feshbach projection operator approximation. The photo-ionization cross sections have been evaluated with and without relativistic effects included into the R-matrix numerical procedures, while the allowance for both quantum interference between dielectronic and radiative recombination, and overlapping resonances has been done utilizing results from the earlier R-matrix Floquet calculation. We discuss all these results with respect to the effect of quantum interference term on the energy dependence profile of photo-recombination cross section for studied transitions.     

Rydberg states of HCN observed by electron impact spectroscopy

The electron energy loss spectrum of HCN has been determined in the energy region 8–13.6 eV at impact energies of 100, 50 and 30 eV. It is shown that energy loss spectra of HCN at intermediate impact energies can be satisfactorily analysed unlike the diffuse unassigned optical absorption spectra that have previously been reported. Rydberg series have been assigned using term values and quantum defects together with ionization potentials obtained by photoelectron spectroscopy.     

A multi-reference CI study of the low-lying valence and Rydberg states of CF3 radical

Highly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD?+?Q) have been performed to study some low-lying valence and Rydberg states of the CF₃ radical. Our highest level results (at the MR-CISD?+?Q level) yield the following energy ordering: 3s (7.90?eV)?2A₂ (8.61?eV)?π (8.72?eV)?z (8.73?eV). MR-CISD results indicate transitions of similar intensities from the ground to the following three final states, in the following order: 3p_π?>?3p_z?>?3s. It has also been found that the aforementioned Rydberg states should be responsible for visible emissions and correspond to transitions between bound states. Therefore, it is suggested that the lack of vibrational structure in the visible band of parent systems (e.g. CF₃Cl) may be due to a transition from a bound to an unbound state of the parent molecule.