Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

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     

Vacuum UV emission by electronically-excited N2: The radicative lifetime of the N2(a′1Σ−u state

A measurement of the electronic transition moment variation for the N₂(a'¹Σ^?_uX¹Σ^+g) band system has allowed a reassessment of the radiative lifetime of N₂(a′). Relaxation to N₂(a′,υ=0) is established as the major channel for quenching of N₂(a¹Π_g, υ = 0) molecules by Ar.     

Energy transfer processes in reactions of He(2 3S) and Ne(3P0,2) with CS2

A comparative spectroscopic study in the visible and ultraviolet ranges was conducted on the flowing afterglows resulting from the reactions of He(2 ³S) and Ne(³P_0,2) metastables with CS₂. Penning ionization was found to be the predominant energy transfer process. However, electron—ion recombination within the afterglows constitutes a major secondary process and gives rise to the most intense emitting system, CS(A ¹ Π → X ¹Σ⁺). Both afterglows were found to produce the CS⁺₂($\text{B}$²Σ⁺_u-$\text{X}$²Π_g), CS⁺₂($\text{A}$²Π_u-$\text{X}$²Π_g) and CS(a ³Π-X ¹Σ⁺) emission systems as well as some atomic sulfur emission lines. Some intensity differences were observed and are interpreted in terms of energetics and the formation mechanisms of the emitting species. A moderately strong CS⁺(A ²Π_i-X ²Σ⁺) emission system was also observed in the ehlium afterglow. In addition, a weak, sharp group of bands in the 390–420 nm range in the helium afterglow has been determined to be due to the presence of a small amount of He⁺ ions. This group of bands consists of two overlapping emission systems and are identified as CS(B ¹Σ⁺ → A ¹Π) and CS⁺(B ²Σ⁺ → A ²Π_i).     

The predissociation of Li2 b3Πu by a3Σ+u

⁶Li₂ 1³Δ_g(F₁) → b³Π_u(F₁v = 0–11) rotationally resolved fluorescence spectra are recorded following perturbation-facilitated optical—optical double resonance excitation of 1³Δ_g via spin—orbit mixed A¹Σ⁺_u ∼ b³Π_u(F₁e) intermediate levels. The f-symmetry Λ-components of b³Π_u(F₁) are broadened above the 0.05 cm⁻¹ detection threshold owing to predissociation by the vibrational continuum of the a³Σ⁺_u state. The observed v = 0–11, N = 31f level widths were used to determine the potential energy curve for the Li₂ a³Σ⁺_u state in the region 2.35 < R < 2.60 Å and 11200 < E < 14900 cm⁻¹ (relative to E = 0 at the minimum of X¹Σ⁺_g). The a³Σ⁺_u ∼ b³Π_u curve crossing is at R = 2.57 Å and E = 11246 cm⁻¹ and the electronic part of the − BN·LL-uncoupling matrix element is 〈b Π¦L⁺ ¦aΣ〉 = 1.216H at an R-centroid Rv_bϵ_a = 2.61Å.     

CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

Recombination energy of N22+

The recombination energy of N₂²⁺ has been computed using N₂²⁺, N₂²⁺ and N₂ potential curves from the literature. Vibrational overlaps and energies liberated in the various N₂²⁺³∑^?_g,¹∑_g⁺, ³Π_u, ¹Π_u → N₂⁺(X²∑⁺_g, A ²∑⁺_g, A ²Π_u, B²∑_u⁺,C²∑_u⁺) vibronic transitions have been computed and used as input for determination of the N₂⁺ recombination energy.     

Dissociation of OCS in liquid argon excited by an electron beam. Evidence of S(1S → 3P) and S2(B 3Σ−u → X 3Σ−g) emissions

Optical emission from e-beam excited liquid argon doped with OCS consists of a prominent S₂(B ³Σ^?_u → X ³Σ^?_g) band progression (v′ = 0 to v″ = 5–18 and v′ = 1 to v″ = 4–8), similar to the observation made in an argon matrix, but with a lesser red shift. The time decay of these bands exhibits a fast component (<0.5μs) and a long non-exponential one, extending to 1 ms, that appears to be due to recombination of S(³P) atoms: S(³P) + S(³P) → S₂(B ³Σ^?_u). Spectral study of the slow component (r > 5 μs) shows a peak at 456 nm identified as the S(¹S → ³P) transition. A possible mechanism for this behavior is discussed.     

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.     

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.     

Hyperfine structure measurements in the B3IIo+u—X 1Σ+g electronic transition of Br2

Hyperfine splittings in some band heads of the B—X system of Br₂ were measured using laser molecular-beam spectroscopy. Quadrupole coupling constants were derived: eqQ(⁷⁹Br) = 810.0(5) MHz for X¹Σ⁺_g, v = 1, and eqQ(⁷⁹Br) = 179.1(16) MHz for B³πino⁺u, v' = 13.     

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.     

Laser-induced fluorescence in supersonic nozzle beams predissociation in the Rb2 C1πu and D 1πu states

By exciting Rb₂ in a supersonic nozzle beam with a pulsed dye laser in the C ¹Π_u-X ¹Σ⁺_g and the D ¹Π_u-X ¹Σ⁺_g band system, we find evidence tor different predissociation processes The products appear as follows from the C state, Rb^* (5 ²P_{$\text{3}\text{2}$}) exclusively, and from the D state Rb*(4²D_{$\text{3}\text{2}$}) predominantly, followcd by Rb^*(5 ²P_i-5²S) cascade radiation In addition, a lower bound of D_e(Rb₂X¹Σ⁺_g)? 3939± 10 cm^?1 is obtained.     

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 6Liz A1Σu+ ∼ b3Πu spin—orbit perturbations: Sub-Doppler spectra and steady state kinetic lineshape model

The ⁶Li₂ A¹Σ_u⁺ υ_A = 2, J = 33 and υ_A = 9, J = 20 levels are shown to be spin—orbit perturbed by the b³Π_u υ_b = 9, F₁e N = 32 and υ_b = 15, F₁e N = 19 levels from which an electronic matrix element of <b³Π_oc|H^SO|A¹Σ⁺ > = 0.114±0.006 cm^?1 is determined. Previous estimates of this quantity are shown to be incorrect. Although the main and extra levels are separated by less than the 900 K Doppler width of A¹Σ_u⁺ ? X¹Σ_g⁺ rotational lines, sub-Doppler intermodulated fluorescence and perturbation-facilitated optical—optical double resonance spectra allow direct observation of the separation of main and extra levels. The mixing coefficients and other perturbation parameters are inferred from a steady state kinetic model of the composite main plus extra lineshape.     

First observation of the M 2Σ+ → E2Σ+ (0—0) transition in NO

The emission spectrum of NO excited by electric discharge has been recorded with a high-resolution Fourier transform interferometer. Strong perturbations are observed in the spectrum of the transition M²Σ⁺→ E²Σ⁺ (0—0), due to mixing of the Rydberg state M²Σ⁺(v = 0) with valence states B²Π(v = 22, 23) and L²Π(v = 3). Accurate energies for the M²Σ⁺ rotational levels are given.     

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.     

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.     

The photodissociation of Li2

The absorption of photons by Li₂ from the X ¹Σ⁺_g state to the A ¹Σ⁺_u and B ¹Π_u states is considered and the mechanisms that lead to dissociation are studied quantitatively. Calculations are reported on the direct predissociation of the b ³Π_u state. The significance of accidental predissociation of the A ¹Σ⁺_u state is discussed and a quantal theory of the process is presented.