A study of atom-atom and atom-molecule interactions in the resonance extraction of sodium atoms

The formation of Na(n²L) and Na₂(A¹?_u⁺, B¹Π_u) in sodium vapour(≈10¹⁴–10¹⁵ cm^?3) irradiated by a cw dye laser tuned to the D lines has been studied. The density of excited atoms was determined by measurements of the realtive absorption of 3²P-3²D transitions. These, together with measurements of Na and Na₂ fluorescence intensities, yield rate constants for formation of Na(n²L) and Na₂(A¹?_u⁺, B¹Π_u). The experimental evidence indicates a negligible role for the photorecombination process Na(3²P) + Na(3²S) in populating A¹?_u⁺ and B¹Π_u molecular states. A new stepwise process is proposed to account for excitation to the molecular diffuse band (420–450 nm).     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Non-radiative decay of the benzene 1B2u and 3B1u states

Optic-acoustic measurements on high pressure benzene are presented, and are used to analyse the nature of the decay channels form the highly vibrationally excited ³B_1u state. The vibrationally relaxed benzene ³B_1u state is deactivated by n-pentane with a collisional efficiency of 3 × 10^?5. A model, introducing an intermediate state close in energy to the ³B_1u state, is shown to be in good accord with the results.     

Fluorescence and recombination-emission spectra from S2 formed by ultraviolet laser photolysis of CS2 in an argon matrix at 15 k

Two series of emission bands were observed for the CS₂/Ar(1 : 100–500) system at 15 K with excitation at 257.3 nm. They are assigned to B³Σ^?_u → χ³Σ^?_g and B″³Π_u → X³Σ^?_g of S₂, which was formed by photodissociation of CS₂, CS₂ + hv → CS + S, followed by recombination of two S atoms. The B″³Π_u state has been found 524 cm^-1 lower in energy than B³Σ^?_u     

Some ab initio calculations related to the predissociation of the C2Σu+ state of N2+

Ab initio calculations in the “first-order wavefunction” CI approximation have been performed for several states of N₂⁺ with ²Σ_u⁺, ²Σ_u^?, ⁴Π_u symmetry. A calculation of the electronic factor of the vibronic interaction between the B²Σ_u⁺ and C²Σ_u⁺ states seems to support the suggestion of Tellinghuisen and Albritton that the C state is predissociated by the continuum of the B state through nuclear momentum coupling.     

Theoretical study of the N+2 molecular ion

The Equations of Motion method has been applied in the calculation of potential energy curves for the X²Σ⁺_g, A²Π_u and B²Σ⁺_u states of N⁺₂. Results are also reported for a new dissociative ²Σ⁺_g state. The theoretical curves are directly compared with the experimental ones as well as in terms of spectroscopic constants. The applicability of the Equations of Motion method to this type of problem is critically examined and discussed with regard to the choice of basis set, numerical effort and agreement with experiment.     

1B2u1A1g fluorescence from benzene produced by electron impact (30–1000 eV)

The ¹B_2u → ¹A_1g fluorescence resulting from electron impact (30–1000 eV) on benzene has been studied in the pressure range 10^?4 ?2 × 10^?3 torr. The fluorescence spectrum is compared with the spectrum obtained by other methods. The energy dependence of the absolute emission cross section indicates a small probability for internal conversion from higher singlet states to the ¹B_2u state.     

1B2u1A1g fluorescence from benzene produced by electron impact (0–30 eV)

The ¹B_2u¹A_1g fluorescence of benzene resulting from the impact of low energy electrons (0–30 eV) has been studied in the pressure range 10^?4 ?2 × 10^?3 torr. It is found that the apparent emission cross section near threshold varies linearly with the pressure. A reaction scheme explaining this behaviour is given. From the absolute value of the apparent emission cross section it follows that excitation of the ³E_1u state is by far dominant over excitation of the ¹B_2u state at low electron impact energies.     

Radiative lifetimes of the B1Π11 states of Li2

Model potential calculations of the B¹Π_uX¹Σ⁺_g transition dipole moment are used in conjunction with the empirical potential energy curves of Vidal and Hessel to calculate the radiative lifetimes of the vibrational levels of the B¹Π_u state. The lifetimes are nearly independent of the vibrational quantum number with a value between 8 and 9 ns.     

The potential energy curve for the B1IIu state of Li2

Multiconfiguration self-consistent field calculations of the potential curve for the B¹Π_u state of Li₂ show a 700 cm^?1 high hump at 5.365 Å in good agreement with experimental estimates of 930 ± 300 cm^?1 and 523 ± 50 cm^?1.     

The dissociation energies of gaseous Br2 and I2

New rotational analyses have been made of the B³Π_0⁺u—X¹Σ⁺_g systems of ⁷⁹Br₂, ⁸¹Br₂ and ¹²⁷I₂. The density of vibrational states near the dissociation limit in the upper states follows the LeRoy—Bernstein predictions for n = 5. From short extrapolations, the ground state dissociation energies are found to be: D₀(⁷⁹Br⁸¹Br) = 15895.6 cm^?1, D₀(¹²⁷I₂) = 12440.1 cm^?1.     

The magnetizability of excited-state hydrogen: temperature-independent paramagnetism in the B1Σ+u state

Components, of the magnetizability tensor for the B¹Σ⁺_u and a ³Σ⁺_g states ot the hydrogen molecule have been calculated for fixed bond lengths near equilibrium. Explicitly correlated “generalised James-Coolidge” type wavefunctions were used. It is found thilt in the B 1Σ⁺_u state the molecular magnetizability is a positive quantity.     

Electronic states of Al2

Ab initio multi-configuration self-consistent field and first-order configuration interaction (FOCI) calculations in an extended basis set have been carried out for the lower energy electronic states of Al₂. The ten core electrons of each Al atom were replaced by an accurate compact effective core potential. The FOCI calculated T_o value for the ³Σ_g^?-³Σ_u^? transition agrees with the experimentally observed emission band to within 90 cm^?1. ³Π_u is calculated to be the electronic ground state of Al₂. Based on FOCI energies and qualitative intensity arguments, the reported optical absorption spectrum of matrix isolated Al₂ also agrees best with a ³Π_u ground state. The ³Σ_g^?1 state is calculated (T_e) at only 324 cm^?1 above the ³Π_u state, and the ¹ΣE_g⁺ state is predicted to lie higher.     

Laser-induced flourescence spectra of YAG-laser vaporized Se2

Rotationally resolved, laser-induced fluorescence spectra of Se₂, cooled to near liquid-N₂ temperature after YAG-laser vaporization of selenium, have been observed. Molecular constants have been obtained for a new O_u state of Se₂. It, along with a l_u component, likely derives from a ³N_u state which has previously been identified as responsible for perturbations of B³Σ^?_uSe₂     

A fano-profile study of the predissociation of the 3pπ D1Πu+ state of H2

The predissociation of H₂ molecules in the 3pπ D ¹Π_u⁺ state has been studied by Fano-profile analysis of the R(0) and R(1) lines from υ = 3 to υ = 11. The predissociation probabilities have been measured. Strong indication of the opening of a new channel of dissociation is reported. Coupling with the B^υB?¹Σ_u⁺ state may be responsible for this.     

A theoretical study of the bound electronic states of the C−2 negative ion

Configuration interaction calculation are employed to study the X ²Σ⁺_g, A ²Π_u, B ²Σ⁺_u, ⁴Σ⁺_u and ⁴Δ_u states of the C^?₂ ion. The results are in good quantitative agreement with experimental findings for the Herzberg—Lagerquist (²Σ⁺_u-²Σ⁺_g) bands and predict a T_e value for the ²Π_u state of only 0.40 eV; corresponding transition moment results are obtained as a function of CC distance. The Cl electron affinity is 3.43 eV, in good agreement with the most recent experimental estimate for this quantity.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

Rate constant for the deactivation of O2 (A3Σu+ by N2

A value of (9.3 ± 1.7) × 10^?15 cm³ molecule ^?1 has been determined as the rate constant for the quenching of O₂(A ³Σ_u⁺) by N₂ at 25°C.     

Production of the n2 herman infrared system by the energy pooling reaction of N2(Δ3Σ+u) metastable nitrogen molecules

Molecular N₂ emission, observed from an Ar(³Po, 2) and Xe(³P₂) + N₂ flowing afterglow apparatus, indicates that the energy pooling reaction by 2N₂(A ³Σ⁺_u) generates the emission from the Herman infrared system, which is an unassigned nitrogen band system. A lower limit to the formation rate constant for the upper state of the Herman infrared system was found to be 2.5 × 10^-11 cm³ molecule^?1 s^?1. The information presented here may help in the identification of the upper and lower states of the emission system. The 2N₂(A) energy pooling reaction also forms N₂(B³ Π_g, v? 8) but a rate constant cannot be assigned from the present data.