The emission spectrum of the 1B1(π*-n+) state of 1,2-cyclobutanedione excited at 488.0 nm

The spectrum of the emission from the ¹B₁(π^*-n₊) state of 1,2-cyclobutanedione excited at 488.0 nm has been measured. Wavelengths and vibrational assignments are reported for 24 bands between 490 and 550 nm, 12 of which can be identified with hot bands in the absorption spectrum. Prominent bands in the emission spectrum are associated with excitation of V^''₈, the symmetric in-plane carbonyl bend (281 cm⁻¹); v^''₁₂, the asymmetric carbonyl wag (488 cm⁻¹); and v^''₇, a symmetric ring distortion (522 cm⁻¹). Sequences in v₁₃, the ring-twisting vibration, are also prominent; the initial excitation lies in the 13³₃ absorption band, while the emission shows intensity maxima for v^'₁₃ = 0 and 2, and a bimodal vibrational relaxation is suggested.     

An ab initio study of the E 3Πg state of the iodine molecule

The E (3)Π(g) state of the iodine molecule is studied by ab initio multireference methods coupled with effective core potentials and large basis sets. Two potential minima are found, a global featuring an ion-pair character, and a local presenting a purely Rydberg nature. Four avoided crossings along the dissociation coordinate attribute an interesting topology to its potential energy curve, and their effect on the vibrational levels of I(2) is discussed.     

Rotationally resolved (3 + 1) rempi of H 2 via the B1Σ+u state

In the paper, we compare the results of our ab initio calculations for the ro-vibrational branching ratios resulting from a (3+1) REMPI of H₂ via the B¹Σ⁺_u state with the experimental data of Pratt, Poliakoff, Dehmer and Dehmer. These results indicate that non-Franck-Condon effects are less important here than in the (3+1) REMPI of H₂ via the C¹Π_u state. We observe that the ΔJ = ±3 peaks in the photoelectron spectrum are of negligible strength and that the ratio of ΔJ = +1 to ΔJ = −1 peak is independent of the ionic vibrational state. A detailed analysis indicates that these features arise as a result of a dynamic interference between the do and dμ ionization channels and do not imply either the smallness of the d-wave or the smallness of the j_t = 3 angular momentum coupling terms.     

Formation of ultracold Rb2 molecules in the v' = 0 level of the a(3)Σ+(u) state via blue-detuned photoassociation to the 1(3)Π(g) state

We report on the observation of blue-detuned photoassociation in Rb(2), in which vibrational levels are energetically above the corresponding excited atomic asymptote. (85)Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 1(3)Π(g) state at a rate of approximately 5 × 10(4) molecules s(-1). We have observed most of the predicted vibrational levels for all four spin-orbit components; 0(+)(g), 0(-)(g), 1(g), and 2(g), including levels of the 0(+)(g) outer well. These molecules decay to the metastable a(3)Σ(+)(u) state, some preferentially to the v' = 0 level, as we have observed for photoassociation to the v' = 8 level of the 1(g) component.     

Experimental verification of strong rotational dependence of fluorescence and predissociation yield in the b1Πu(v = 1) level of 14N2

New, rotationally resolved fluorescence-excitation spectra confirm coupled-channel Schro?dinger-equation predictions of strong rotational dependence of the fluorescence and predissociation yields in the b(v = 1) level of (14)N(2).     

Pseudo-Jahn-Teller effect as the origin of the exalted frequency of the b2u Kekulé mode in the 1(1)B2u excited state of benzene

In this paper we show that a pseudo-Jahn-Teller (PJT) coupling between the (1)A1g ground state and the (1)B2u excited states along the Kekulé mode of b2u symmetry is responsible for the surprisingly low frequency of this mode in the ground state and its remarkable upward shift of 261 cm(-1) upon excitation to the first (1)B2u excited state.     

Potentials of the D¹0u⁺ (6¹S₀) and F³1u(6³P₂) electronic Rydberg states of Cd₂ from ab initio calculations and laser-induced fluorescence excitation spectra

The method of supersonic free-jet expansion beam combined with techniques of laser spectroscopy was used in an investigation of vibronic and isotopic structures in the D10(u)? (61S?) and F31(u)(63P?) electronic energy Rydberg states of Cd?. Laser-induced fluorescence excitation spectra recorded using the D10(u)? ← X10(g)?(51S?) and F31(u) ← X10(g)? transitions in the region of 206-218 nm provided spectroscopic characteristics of the excited states and allowed constructing of their intratomic potentials. Isotopic structures recorded in the (υ',υ') bands of the D10(u)? ← X10(g)? transition were used in determination of the D10(u)? state vibrational characteristics (ω'(e)x'(e), ω'(e)x'(e)) and υ' assignment. The ν(0,0) recorded directly in the F31(u) ← X10(g)? transition enabled determination of the bottom of the F31(u) state potential well. Valence ab initio calculations of Cd? interatomic potentials were performed with relativistic and spin-orbit effects taken into account. The experimental results were compared with results of the ab initio calculations. A free-jet expansion of Cd? as a source of entangled atoms for a test of Bell's inequality was analyzed.     

Time-resolved photoelectron studies of the relaxation of the S1(1E′') excited state of sym-triazine

We present photoelectron spectra of the lowest singlet state (¹E′') of sym-triazine obtained with 2 ns and 5 ps excitation sources. Comparisons of picosecond and nanosecond spectra are made at three wavelengths, corresponding to the 6₀¹, 6₀² and the 6₀¹12₀¹ vibrational levels. The spectra show that rapid (</ 5 ps) relaxation to the lowest triplet state occurs subsequent to singlet excitation. Coupling of S₁ levels to the T₁ manifold is very inhomogeneous with intersystem crossing rates ranging from 10⁷ s⁻¹ to > 10¹¹ s⁻¹. Furthermore, for excitation at the 6₀¹12₀¹ level we find evidence for relaxation to another excited state at rates ⩾ 10¹¹ s⁻¹.     

Nodal surfaces of the wave functions of the hydrogen molecule in the triplet state 3Σu +

For molecular hydrogen in the triplet state ³Σ_u ⁺, the nodal surfaces of the wave function corresponding to the minimum basis set of Slater orbitals in the Hartree—Fock approximation and those of the wave function used in calculations by the diffusion quantum Monte Carlo method were plotted and analyzed. Taking account of the condition for antisymmetrical wave function of the triplet state ³ S of He atom, the Hartree-Fock approximation in the minimum basis set of one-electron orbitals is inappropriate for a priori determination of the nodal surfaces of many-electron wave functions (MWF). An MWF quantum chemical method developed by the authors is outlined. The alternative nodal surfaces for H₂ (³Σ_u ⁺) a priori specified in this method are presented.     

High resolution study of the E(0+g) → B3Π (0+u) transition (4400-4000 Å) of I2

The E → B transition of I₂ in the region 4400-4000 Å has been studied under high resolution using a 7.3 m vacuum Ebert spectrograph in the 14th order. The values of the constants B_e, α_e, γ_e, D_e and β_e of both E and B states determined from the analysis of the rotational structure of nine bands of the system are presented. Vibrational constants of the E state obtained from the analysis of all the bands so far reported and consistent with the precise constants of the B state given in previous work are also presented. The origin of the upper state, E(0⁺_g), of the transition is discussed.     

Electronic spectra and predissociation of jet-cooled CH3O and CH3O-Ar in the Ã2A1 state

The òA₁-X̃²E electronic spectrum of jet-cooled methoxy radical has been examined by the LIF technique. Two newly discovered vibrational bands of 2930 and 1390 cm⁻¹ are assigned to ν₁ (totally symmetric C-H stretching) and a degenerate ν₅ mode, respectively. The predissociation, CH₃O → CH₃ + O in the òA₁ state is newly elucidated and the threshold energy is deter- mined as 5100 cm⁻¹ from the potential minimum. For the CH₃O-Ar complex, the threshold energy is reduced by about 100 cm⁻¹.     

Laser-induced photoionization of Ar2(3Σu+) at 308 nm

Experimental evidence is provided to show that the Ar₂(³Σ⁺_u) excimer is photoionized by absorption of light at 308 nm. This direct photoionization of Ar₂(³Σ⁺_u) was used to measure the distribution of atomic states belonging to the Ar(3p⁵4p) electronic manifold produced in dissociative recombination of Ar₂⁺(²Σ_u⁺) at atmospheric pressure. It was found that electronically excited states, Ar(2p₂) and Ar(2p₁₀), accounted for 96% of the excited state population of the Ar(3p⁵4p) configuration produced in dissociative recombination. The Ar₂(³Σ_u⁺) state is also photodissociated directly at 308 nm producing electronically excited Ar atoms more energetic than the Ar(3p⁵4p) configuration.     

Electron impact excitation of the ã (3)B(1u) electronic state in C2H4: an experimentally benchmarked system?

We report on differential and integral cross section measurements for the electron impact excitation of the lowest-lying triplet electronic state (a? (3)B(1u)) in ethylene (C(2)H(4)). The energy range of the present experiments was 9 eV-50 eV, with the angular range of the differential cross section measurements being 15°-90°. As the ground electronic state of C(2)H(4) is a (1)A(g) state, this singlet → triplet excitation process is expected to be dominated by exchange scattering. The present angular distributions are found to support that assertion. Comparison, where possible, with previous experimental results from the University of Fribourg group shows very good agreement, to within the uncertainties on the measured cross sections. Agreement with the available theories, however, is generally marginal with the theories typically overestimating the magnitude of the differential cross sections. Notwithstanding that, the shapes of the theoretical angular distributions were in fact found to be in good accord with the corresponding experimental results.     

Alignment effect of N2(A3Σu+) in the energy transfer reaction of aligned N2(A3Σu+) + NO(X2Π) → NO(A2Σ+) + N2(X1Σg+)

Steric effect in the energy transfer reaction of N(2)(A(3)Σ(u)(+)) + NO(X(2)Π) → NO(A(2)Σ(+)) + N(2)(X(1)Σ(g)(+)) has been studied under crossed beam conditions at a collision energy of ~0.07 eV by using an aligned N(2)(A(3)Σ(u)(+)) beam prepared by a magnetic hexapole. The emission intensity of NO(A(2)Σ(+)) has been measured as a function of the magnetic orientation field direction (i.e., alignment of N(2)(A(3)Σ(u)(+))) in the collision frame. A significant alignment effect on the energy transfer probability is observed. The shape of the steric opacity function turns out to be most reactive at the oblique configuration of N(2)(A(3)Σ(u)(+)) with an orientation angle of γ(v(R)) ~ 45° with respect to the relative velocity vector (v(R)), which has a good correlation with the spatial distribution of the 2pπ(g)* molecular orbital of N(2)(A(3)Σ(u)(+)). We propose the electron exchange mechanism in which the energy transfer probability is dominantly controlled by the orbital overlap between N(2)(2pπ(g)*) and NO(6σ).     

Microcalorimetric Study of the Biological Effects of Zn~(2+) on Bacillus thuringiensis Growth

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Predissociation and hyperfine structure of the B3Πou+ state of Br2

Using molecular-beam laser spectroscopy, the hyperfine structure of the B-X system of ⁷⁹Br₂ was measured to obtain reliable data on hyperfine and rotational predissociation for the levels B(0_u⁺) ν = 11, 13 and 16. We report the first measurement of the hyperfine predissociation with no rotational predissociation on P(1) transitions. The unexpected strongly J-dependent variation of the predissociation parameters leads to the conclusion that the familiar theory describing all known data for the B state of iodine may be inadequate for bromine.     

Photoelectron imaging spectroscopy of S1(1B2u π,π*) benzene via 6(1)1n (n = 0-3) levels

We report resonance-enhanced two-photon ionization photo-electron spectroscopy of jet-cooled benzene via the 6(1)1(n) (n = 0-3) vibronic levels in S(1)((1)B(2u) π,π*) using a nanosecond UV laser and photoelectron imaging. The best energy resolution (ΔE/E) was 0.7%. The photoelectron spectrum from the S(1) 6(1)1(3) level (E(vib) = 3284 cm(-1)) in the channel three region exhibited a clear signature of intramolecular vibrational redistribution (IVR). The spectral features were consistent with picosecond zero kinetic energy photoelectron (ZEKE) spectra reported by Smith et al. [ J. Phys. Chem. 1995, 99, 1768]. The photoelectron angular anisotropy parameter β(2) was found to be negative in ionization from the 6(1)1(n) (n = 0-3) levels with photoelectron kinetic energies up to 5000 cm(-1). No influence of a shape resonance was identified.     

Laser excitation spectrum of the 0g+(X 1Σg+)−0u+(3Πu) transition in Cd2

Spectroscopic constants and bond strengths of ground-state 0_g⁺(¹Σ_g⁺) and excited state 0_u⁺(³Π_u) Cd₂ van der Waals molecules have been determined by laser excitation of Cd₂ spectra in a supersonic expansion of cadmium vapor.     

Study on the reaction of triple helix poly(A:2I) with Cu~(2+)

The effect of Cu2+ on the triple-stranded helical structure of poly(A:2I) was studied by means of circular dichroism spectral method with the help of ultraviolet spectral and ethidium bromide fluorescence probe methods. It was found that Cu2+ destabilizes the structure of the triple helix poly(A:2I) and induces its structural transformations, meanwhile, the transformations can be partially reversed by a higher NaCl concentration. The structural transformations may be expressed by the following scheme: poly(A:2I) - poly(A:I) + poly(I)- poly(A) + 2poly(I)