Vibrational analysis of the a3Σ+-X1Σ+ and b3Π-X1Σ+ band systems of GeS

Spectra of GeS have been obtained in a chemiluminescent flame produced by the reaction Ge + OCS → GeS + CO. Neither of the known band systems, D¹Π-X¹Σ⁺ and E¹Σ⁺-X¹Σ⁺, was observed, but two new band systems in the regions 350–400 and 420–650 nm were obtained. By comparison with similar systems in isovalent molecules, these were assigned as b³Π₁-X¹Σ⁺ and a³Σ⁺-X¹Σ⁺, respectively. Vibrational assignments were made with the help of the germanium isotope effect and vibrational constants were obtained for the states involved. Approximate Morse potential Franck-Condon factors were computed and were shown to fit the general trend of the intensity distribution for both systems. Addition of active nitrogen to the flame was shown to increase the intensity of the b-X system by an order of magnitude while hardly affecting the a-X system. Constants (in cm^?1) obtained for the two new states are: a³Σ⁺: T_e = 21986.3 ± 2.3, ω_e = 388.9 ± 1.0, ω_ex_e = 1.35 ± 0.11; b³Π₁: T_e = 27192.0 ± 1.8, ω_e = 435.4 ± 1.1, ω_ex_e = 1.68 ± 0.20.     

Fourier Transform Emission Spectroscopy of the FΣ-XΣ System of RuN

Emission spectra of RuN have been recorded at high resolution in the region 12 000-35 000 cm⁻¹ using a Fourier transform spectrometer. The molecules were excited in a ruthenium hollow cathode lamp in the presence of about 2.5 Torr of Ne and 5 m Torr of N₂. New bands with origins near 17 758.1, 18 866.4, 19 800.4 and 20 721.5 cm⁻¹ have been assigned as the 0-1, 0-0, 1-0, and 2-0 bands of a new ²Σ⁺-²Σ⁺ system with the lower state as the ground state. This transition has been labeled as F²Σ⁺-X²Σ⁺, with the F²Σ⁺ state arising from the 1σ²2σ²1π⁴1δ⁴4σ¹ configuration. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted. The principal equilibrium constants for the ground state of RuN are ΔG(1/2)″=1108.3235(22) cm⁻¹, B_e″=0.5545023(42) cm⁻¹, α_e″=0.0034468(57) cm⁻¹, r_e″=1.5714269(60) Å, while the equilibrium constants for the excited state are ω_e′=946.8471(40) cm⁻¹, ω_ex_e′=6.4229(14) cm⁻¹, B_e′=0.50085(21) cm⁻¹, α_e′=0.00375(10) cm⁻¹, r_e′=1.65345(34) Å. This transition is analogous to the E²Σ⁺-X²Σ⁺ system of RhC (W. J. Balfour et al., J. Mol. Spectrosc.198, 393 (1999)).     

Radiative corrections to the reactione + e -→e + e -π+π-

The radiative corrections to the reactione ⁺ e ^-→e ⁺ e ^-π⁺π^- are calculated to order α⁵ for an experiment without electron tagging and where the acceptance of the central detector is limited by angular and momentum cuts. The total radiative correction is found to be smaller than a few percent from 1.5 to 70 GeV.     

Extension of the rotational analysis of the 1Π-X1Σ+ system of AsN

Rotational analysis of bands with v′ = 0 through 3, in the ¹Π-X¹Σ⁺ system as the AsN molecule, has been carried out. Rotational constants for the X¹Σ⁺ state are: B_e = 0.54551 cm^?1, α_e = 0.003366 cm^?1 and D_e = 5.3 × 10^?7cm^?1. Strong perturbations are observed in the upper levels and the resulting B_v curves are plotted against J.     

The A2Π-X2Σ+ emission spectrum of zinc deuteride

The A²Π-X²Σ⁺ emission of ZnD was studied at moderate and high resolution in the region 346–505 nm. A detailed rotational analysis of 10 bands has been performed using the ²Π formulas of Mulliken and Christy, with the Almy and Horsfall centrifugal distortion term. The principal molecular constants for the X²Σ⁺ state are (cm^?1): B_e = 3.3990, α_e = 0.0964, D_e = 1.16 × 10^?4, β_e = 6.4 × 10^?6, γ₀ = 0.122, ω_e = 1141.54, ω_ex_e = 24.29, and, for the A²Π state, T_e = 23 280.55, B_e = 3.7772, α_e = 0.0868, D_e = 1.14 × 10^?4, A₀ = 343.29, p₀ = 0.149, q₀ = 1.53 × 10^?3, ω_e = 1361.49, and ω_ex_e = 20.69. RKR potential curves and A-X Franck-Condon factors were calculated. A comparison was made with the spectrum of ZnH and the isotopic splitting for ⁶⁴ZnD, ⁶⁶ZnD, and ⁶⁸ZnD is briefly discussed.     

Determination of the radiative widths of the η′ and A2 from two-photon exchange production

From the two-photon exchange processes e⁺e^? → e⁺e^?η' (958) → e⁺e^??⁰γ and e⁺e^? → e⁺e^?A₂ (1310) → e⁺e^?π⁺π^?π⁰ observed using the CELLO detector at PETRA the radiative widths of the η' and A₂ have been determined with the results: Γ_γγ(η') = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γ_γγ(A₂) = 0.59 ± 0.14[stat.] _?0.08^+0.31[syst.] keV.     

A measurement of the reaction e+e- →e+e-η′ and the radiative width Γη′→γγ at petra

The reaction e⁺e^- → e⁺e^-η' has been observed in the JADE experiment at PETRA, by detecting the final state π⁺π^-γ, resulting from the decay η' → γ?⁰. The cross section was measured at an average beam energy of 17.15 GeV to be σ(e⁺e^- → e⁺e^-η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ_η'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.     

The electronic spectrum of bismuth monofluoride: An 0+ ← X10+ band system at 3838 Å

Emission bands of BiF (in the region of 3800 Å), formerly designated as belonging to the B-X₁0⁺ and A₃-X₁0⁺ transitions, have been photographed and rotationally analyzed under high resolution. These bands have been found to belong to an 0⁺ ← X0⁺ system. Extensive rotational and vibrational perturbations have been observed and the nature of the perturbing state is discussed.     

New spectroscopic studies of the Comet-Tail (AΠi-XΣ) system of the CO molecule

In the electronic emission spectrum of the ¹²C¹⁶O⁺ molecule, 11 bands of the Comet-Tail (A²Π_i-X²Σ⁺) system have been recorded and analyzed. Spin splitting in most of the observed lines of the 0-2, 1-0, 2-0, 2-1, 3-0, 4-0, 4-2, 6-0, 7-0, 7-1, and 8-1 bands, comprising nearly 3400 lines, has been recorded under high resolution by conventional spectroscopy. The rotational analysis of bands has been performed by nonlinear least-squares procedures and by means of effective Hamiltonians of Brown et al. and the rovibronic structure parameters have been obtained. The data of bands of the A-X system and earlier analyzed bands of the B-X and B-A systems have been merged together. As a result of this global fit, the state of information about the energy structure has been significantly enlarged for the A state and enlarged and improved for the X state. Also RKR potential curves for both states and Franck-Condon factors as well as r-centroids of the Comet-Tail system of CO⁺ have been calculated.     

The spectra and structure of indium iodide: The rotational and vibrational constants of the B 1 state

The rotational constants of the B 1 state of indium iodide are reported for the first time as B_e = 0.037533 cm⁻¹ and α_e = 0.000289 cm⁻¹ while T_e = 25050.60 cm⁻¹ for the B1-X0⁺ transition. Accurate vibrational constants are also computed from measured Q heads as ω_e= 146.36 cm⁻¹ and ω_eχ_e = 2.20 cm⁻¹.     

Laser spectroscopy of the B[21.68]8-X8, B′[21.65]8-X8 and C[22.3]7-X27 transitions of holmium monofluoride

The spectrum of holmium monofluoride (HoF) in the blue (420-480 nm) region has been studied using laser-induced fluorescence. Previous work [J. Phys. B 7 (1974) L234] had assigned several bands in this region to the B8-X8 transition. By obtaining wavelength selected laser excitation spectra at high resolution and rotationally analyzing seven bands in this region, we have shown that not all the bands previously assigned to the B8-X8 system belong to the same electronic transition and have identified three separate transitions which we have labelled B8-X8, B′8-X8, and C7-X₂7. Preliminary low resolution dispersed fluorescence spectra have shown several excited states at energies greater than 4000 cm⁻¹ above the ground state and, though not all could be assigned, ligand field theory calculations are consistent with assigning them to the first excited spin-orbit component of the Ho⁺(4f¹⁰6s²)F⁻ ground state configuration or to the first excited configuration, Ho⁺(4f¹¹6s)F⁻. The results of the dispersed fluorescence experiments also tentatively place the X₂7 state at ∼70 cm⁻¹ above the ground X7 state.     

Spontaneous radiative dissociation in molecular hydrogen

The spontaneous radiative dissociations of the discrete vibrational levels of the B¹Σ⁺_u electronic states of H₂, HD and D₂ of the C¹Π_u electronic state of H₂ into the vibrational continuum of the ground X¹Σ⁺_g state are calculated as a function of the emission wavelength. The fluorescent spectra of HD in the Lyman system and of H₂ in the Werner system resulting from an excitation source uniform in wavelength are predicted. The vibrational radiative lifetimes are tabulated as are the fractions of radiative decays that lead to dissociation. The effects of centrifugal distortion are discussed briefly. An appendix describes a sum rule used to check the numerical accuracy of the calculations.     

Examination of two new low-lying electronic states of SiS observed in chemiluminescent flame spectra

Diatomic silicon sulfide molecules have been produced in the chemiluminescent reaction of silicon atoms with OCS. Spectra of the resulting flame consist mainly of two new band systems in the region 350–400 and 385–600 nm. These systems have been assigned as b ³Π_r-X ¹Σ⁺ and a ³Σ⁺-X ¹Σ⁺ on the basis of band structure, spin-orbit splitting, molecular constants, and comparison with chemiluminescent spectra of isovalent molecules. Vibrational assignments were made with the help of the isotope effect and vibrational constants were obtained. Rotational structure was observed in some a-X bands and a partial analysis yielded an approximate rotational constant, B 0.247 ± 0.007 cm⁻¹, for the a ³Σ⁺ state. Franck-Condon factors, calculated for the a-X system, are shown to fit the general trend of the intensity distribution. Irregularities in spin-orbit splitting and in relative intensities of the spin-orbit components of the b ³Π-X ¹Σ⁺ system were observed and an attempt is made to explain them in terms of interactions with neighboring states. Addition of active nitrogen to the flame was shown to greatly increase the intensity of the b-X system relative to the a-X system. Constants (in cm⁻¹) obtained for the new state are: a³σ⁺: T_e=24 582.1 ± 1.3, ω_e=503.8±1.0, ω_ex_e=1.86±0.21b³σ⁺: T_e=27 314.5 ± 2.2, ω_e=619.4±2.0, ω_ex_e=5.75±0.52b³σ⁺: T_e=27 407.9 ± 1.1, ω_e=524.3±1.2, ω_ex_e=3.97±0.28     

Rotational analysis of the A2Πi → X2Πr band system of the sulfur monoxide cation,SO+

Six bands in the 0-v″ progression and three bands in the 1-v″ progression of the A²Π_i → X²Π_r visible system of SO⁺ have been recorded photoelectrically and rotationally assigned. Molecular constants for v′ = 0 and 1 in the A state and for v″ = 4–9 in the X state have been obtained using direct fitting and merging techniques.     

Analysis of the Comet-Tail (AΠi-XΣ) Bands of CO

In the electronic emission spectrum of the isotopic carbon monoxide ion ¹³C¹⁶O⁺ molecule, seven bands of the comet-tail (A²Π_i-X²Σ⁺) system have been recorded and analyzed. The spin splitting in most observed lines of the bands 1-0, 2-0, 3-0, 4-0, 5-0, 2-1, and 7-1 comprising over 1900 lines has been recorded under high resolution by using conventional spectroscopy. The rotational analysis of bands has been performed by nonlinear least-squares procedures and by means of effective Hamiltonians of Brown et al., the rovibronic structure parameters have been obtained. As a result of multistaged and merged analysis of the currently obtained bands of the A-X system and of the bands of the B-X system obtained earlier the state of information about the energy structure has been significantly enlarged for the A state and enlarged and improved for the X state. Also RKR potential curves have been calculated for both states and Franck-Condon factors as well as r-centroids of the comet-tail system of ¹³C¹⁶O⁺.     

High-resolution visible laser spectroscopy of HfF

The electronic spectrum of hafnium monofluoride has been investigated from 415 to 725 nm using a laser-ablation/molecular beam laser-induced fluorescence spectrometer. Several electronic systems were observed and data have been recorded at both low and high resolution. High resolution rotational analyses of the [17.4]1.5-X1.5 (0-0), [17.9]2.5-X1.5 (0-0), [19.7]0.5-X1.5 (0-0), [20.0]0.5-X1.5 (0-0), [21.1]2.5-X1.5 (0-0), [22.3]1.5-X1.5 (0-0), and [23.3]0.5-X1.5 (0-0) subbands have been carried out, resulting in accurate values for the ground and excited state effective rotational constants. Furthermore, the rotational analysis of the subbands assigned as [17.4]1.5-X1.5 (1-0) and [17.9]2.5-X1.5 (1-0) allows us to determine values of 589.7569(6) and 588.9076(6) cm⁻¹ for ΔG^′_1/2 [17.4] and ΔG^′_1/2 [17.9], respectively. From dispersed fluorescence data we find that ΔG^′′_1/2=670(13) cm⁻¹ for the ground state and that another low-lying electronic state lies at ∼2850 cm⁻¹. The data also suggests that a second low-lying electronic state lies at ∼5200 cm⁻¹ above the ground state.     

The Electronic Transition Moment Function for the BΠ-XΔ System of TiO

Several vibronic bands associated with v′=0, 1, and 2 for the B³Π-X³Δ transition of TiO have been observed using a dispersed laser induced fluorescence (DLIF) technique. From intensity distributions of the DLIF spectra, the dependence of the electronic transition moment R_e(r) for the B³Π-X³Δ system was determined as a function of the internuclear distance r. For the determination of the R_e(r) function, a merged fit of the observed distributions, the reported radiative lifetimes of three vibrational levels in the B³Π state, and the reported value of R_e(r) for the (0, 0) band were performed; R_e(r) was determined as R_e(r)=1.3723(79)[1−0.316(81)(r−r₀)+2.0(10)(r−r₀)²](r₀=1.6648 Å and 1.5131 Å≤r≤1.8636 Å). The r-dependence of R_e(r) was much smaller than the reported theoretical predictions. The obtained values of R_e(r) were analyzed simultaneously with the hyperfine coupling constants for the X³Δ state and the spin-orbit constants for the X³Δ and B³Π states to assess the ionic and orbital characters. It was found that the r-dependence of R_e(r) could be accounted for by both the configuration interaction in the B³Π state and the polarization in the unpaired 9σ and 4π orbitals.     

Investigation of negative ion states in HCl and HF by configuration interaction methods

Multi-reference configuration interaction calculations are employed for the study of Born-Oppenheimer potential energy curves in HF/HF^- and HCl/HCl^-. Large gaussian basis sets including negative ion functions as well as diffuse s, p and d AOs are employed thereby. In HCl^- a repulsive 2Σ⁺ state emerges from the calculations approximately 4·2 eV above the HCl X ¹Σ⁺ ground state; no such entity could be observed in HF^- in the energy range treated. All other CI roots which produce potential curves parallel to and above the X ¹Σ⁺ curve are found to possess quite diffuse charge distributions in the basis set variations undertaken and can therefore not be considered resonant states but rather as discrete representations of free-electron species in the HX + e^- continuum. For large internuclear distances the HF^- and HCl^- curves lie below those of the neutral species, whereby the crossing between the X ²Σ⁺ ionic and X ¹Σ⁺ curves are calculated to occur at 3·2 a ₀ in HCl/HCl^- and 2·6 a ₀ in HF/HF^-. Finally it is argued that non-adiabatic effects involving the low energy HX^- continuum states in the Born-Oppenheimer approximation and the bound HX^- species at large internuclear separations (with continuation inside the HX potential well) are ultimately responsible for observed electron scattering resonances, in accordance with recent work of Domcke and Cederbaum and of Nesbet.     

Coulomb effects in spatially separated electron and hole layers in coupled quantum wells

We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/Al_xGa_1?x As coupled quantum wells (CQWs) at low temperatures (T = 1.4 K) for a broad range of electron-hole (e-h) densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the e-h density both for a zero magnetic field and at high fields for all Landau level transitions; this is in contrast to the electron-hole systems in single QWs where the main features are explained by the band-gap renormalization resulting in a reduction of the PL energy. The observed enhancement of the ground state energy of the system of the spatially separated electron and hole layers with increasing the e-h density indicates that the real space condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has been observed: its relative intensity increased both in PL and in absorption (measured by indirect PL excitation) with increasing density; its energy separation from the direct exciton line fits well to the X ^? and X ⁺ binding energies previously measured in single QWs. The line is therefore attributed to direct multiparticle complexes.