Vibrational energy transfer from N2 to CO on electron excitation of N2-CO solids at 4.2 K

Spectra emitted from 0.1% CO-N₂ solids excited with high energy electrons at 4 K show evidence for resonant transfer of vibrational energy from highly excited vibrational levels of N₂ to CO in the process N₂(X¹Σ_g⁺, ν) + CO(ν = 0) → N₂(X¹Σ_g⁺, ν - 1) + CO(ν = 1) + phonons. Energy transfer from levels with ν ? 9 has been observed.     

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).     

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.     

Dynamics of reactions of O(3P) atoms with CS,CS2 and OCS

The reactions of CS(X ¹Σ⁺), CS₂(X ¹Σ⁺_g) and OCS(X ¹Σ⁺) with O(³P) were studied at 298 K by means of a CO laser resonance absorption technique. The CO(ν) population distribution produced from the reaction O(³P) + CS(X ¹Σ⁺) studied in a quartz flash photolysis tube (λ>/ 200 nm) is similar to distributions observed previously for ν> 7. For ν < 7 an energetically colder vibrational population was observed which is attributed to the reaction of O(³P) atoms with undissociated CS₂(X ¹Σ⁺_g). Subsequent experiments carried out in a Pyrex flash photolysis tube (λ>/ 300 nm) in which the O(³P) + CS₂(X ¹Σ⁺_g) reaction is the only one which can occur confirmed that the colder population observed is attributable to this process. The branching ratio for the reaction channel O(³P) + CS₂(X ¹Σ⁺_g) → CO(X ¹Σ⁺) + S₂(³Σ^?_g) has been measured. We find that 1.4 ± 0.2% of the O + CS₂ reaction proceeds through this channel, and that the rate constant for this reaction channel is, k = 3.5 (±0.5) × 10¹⁰ cm³/mole s. Isotope labeled experiments using ¹⁸O atoms show that the O(³P) + OCS(X ¹Σ⁺) reaction takes place by a direct stripping mechanism, wherein CO(ν) is produced exclusively from the parent OCS molecule. The CO(ν) formed in this reaction carries about 9% of the total available energy.     

Kinetic studies of the deactivation of O2(1Σg+) and O(1D)

The kinetics of the deactivation of O₂(¹Σ_g⁺) is studied in real time. O₂(¹Σ_g⁺) is generated in this system by the O(¹D) + O₂ reaction following O₃laser flash photolysis in the presence of excess O₂, and it is monitored by its characteristic emission band at 762 nm. Quenching rate constants were obtained for O₂, O₃, N₂, CO₂, H₂O, CF₄and the rare gases. Since O(¹D) is the precursor for the formation of O₂(¹Σ_g⁺), the addition of an O(¹D) quencher effectively lowers the initial concentration of O₂(¹Σ_g⁺). By measuring the initial intensity of the 762 nm fluorescence signal, the relative quenching efficiencies were determined for O(¹D) quenching by N₂, CO₂, Xe, and Kr with respect to O₂; the results are in good agreement with literature values.     

Theoretical study of the 2Σu+ and 2Σg+ states of Li2− and Na2−

Ab initio calculations are performed to obtain potential energy curves for the X¹Σ_g⁺ state of Li₂ and Na₂ and the X²Σ_g⁺ and A²Σ_g⁺ states of their anions. The A²Σ_g⁺ M₂^? curves are found to intersect the X¹Σ_g⁺M₂ curves at low energies and are expected to play a major role in the e^? + M₂ → M^? + M process.     

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.     

Potential energy surfaces for the photodissociation H2O→O(1Dg + H2(X1Σ+g)

The minimum energy pathways for symmetrical dissociation of water into O(¹D_g + H₂(X¹Σ⁺_g) are calculated by the MRD Cl technique for various excited states of H₂O and possible mechanism for the photodissociation are discussed.     

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.     

The energy balance and branching ratios associated with the chemiluminescent reaction Si(3P) + N2O(1Σ) → SiO*(a3Σ+, b3Π, A1Π) + N2(υ″ ⩾ 5) — possible formation of vibrationally excited N2

Silicon atoms react under single collision conditions with N₂O to yield chemiluminescent emission corresponding to the SiO a³Σ⁺?X¹Σ⁺ and b³Π?X¹Σ⁺ intercombination systems and the A¹Π?X¹Σ⁺ band system. A most striking feature of the SiN₂O reaction is the energy balance associated with the formation of SiO product molecules in the A¹Π and b³Π states. A significant energy discrepancy ( = 10000 cm^? = 1.24 eV) is found between the available energy to populate the highest energetically accessible excited-state quantum levels and the highest quantum level from which emission is observed. It is suggested that this discrepancy may result from the formation of vibrationally excited N₂ in a concerted fast SiN₂O reactive encounter. Emission from the SiO a³Σ⁺ (A¹Π) and b³Π(A¹Π, E¹Σ₀⁺) triplet-state manifold results primarily from intensity borrowing involving the indicated singlet states. Perturbation calculations indicate the magnitude of the mixing between the b³Π, A¹Π and E¹Σ₀⁺ states ranges between 0.5 and 2%. On the basis of these calculations, the branching ratio (excited triplet)/(excited singlet) is found to be well in excess of 500. An approximate vibrational population distribution is deduced for those molecules formed in the b³Π state. The present studies are correlated with those of previous workers in order to provide an explanation for diverse relaxation effects as well as observed changes in the ratio of a³Σ⁺ to b³Π emission as a function of pressure and experimental environment. Some of these effects are attributable to a strong coupling between the a³Σ⁺ and b³Π state. Based on the current results, there appears to be little correlation between either (1) the branching ratio for excited state formation or (2) the total absolute cross section for excited-state formation and (3) the measured quantum yield for the SiN₂O reaction. Implications for chemical laser development are considered.     

De-excitation rate constants of He(2 3S) by atoms and molecules as studied by the pulse radiolysis method

Time-resolved measurement of He (2 ³S) concentration by its optical absorption after electron pulse irradiation of HeN₂ mixtures confirms that the optical emission of N⁺₂(B ²Σ⁺_u → X ²Σ⁺_g) is based on the energy transfer (Penning ionization) from He (2 ³S) to N₂. The addition of other atoms and molecules to HeN₂ mixtures changes the decay rate of the optical emission N⁺₂(B ²Σ⁺_u → X ²Σ⁺_g), which is a detector of He (2 ³S), and gives the rate constant of He (2 ³S) de-excitation by various atoms and molecules. Our results are discussed from the viewpoint of a gas-kinetic collision model.     

Determination of the quenching rates of N2+(B2Σu+, ν = 0,1) By N2 using laser-induced fluorescence

Time-resolved fluorescence laser-induced spectroscopy was used to examine the quenching of the vibrational levels ν = 0 and ν = 1 of N₂⁺(B²Σ_u⁺) by N₂. The rate coefficients of the quenching reactions are found to be constant over the temperature range 300–500 K. The quenching constant for the ν = 1 state was found to be approximately twice the value of the quenching constant of the ν = 0 state.     

Possible production of O2(1Δg) and O2(1Σ+g) in the reaction of NO with O3

High-resolution spectra of the NO₂ continuum emission produced from the reaction NO + O₃ → NO₂ + O₂ have been investigated to detect any possible emission from O₂(¹Δ_g) at 1270 nm or O₂(¹Σ⁺_g) at 762 nm. The photolysis of O₃/O₂ mixtures at 253.7 nm, which produces both states of O₂ with known quantum efficiency, has been used as an internal standard. From the results it is concluded that less than 1/300 and 1/200 of the NO + O₃ reactive collissions result in production of O₂(¹Δ_g) or O₂(¹Σ⁺_g), respectively, at room temperature.     

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.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Reactions of O2(Δg) with ozone

The rate of the reaction O₂(¹Δ_g + O₃ → 2O₂(³Σ ⁻_g) + O(³P) was measured in a static reactor between 296 and 360°K. The decay of O₂(¹Δ_g) was determined from the emission of O₂(¹Σ⁺_g) at 7620 Å. The rate constant is 6.0 × 10⁻¹¹ exp (−5670/RT) cm³ molecule⁻¹ sec⁻¹. The reaction of O(³P) with ozone is found to produce O₂(¹Σ⁺_g) with approximately 0.01% efficiency.     

The effect of internal excitation on the collision induced dissociation of I+2(2Πg,υ) ions

Cross sections for collision induced dissociation of 0.65 to 3.2 keV I⁺₂(²Π_g, υ) ions in I⁺₂(²Π_g, υ) + N₂(X ¹Σ⁺_g, υ = 0) interactions have been determined. Reaction cross sections for I⁺₂(²Π_{$\text{3}\text{2}$,g}, υ) ions in low vibrational levels vary smoothly from 6 to 10 A² with increasing kinetic energy. Dissociation cross sections for I⁺₂(²Π_{$\text{1}\text{2}$,g}, υ) ions are larger than those involving ground state ions. Processes involving highly excited metastable states of I⁺₂ are not observed in this investigation.     

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.     

Resonance-enhanced multiphoton ionization of molecular hydrogen via the E,F1Σg+ state: Photoelectron energy and angular distributions

Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H₂ X¹Σ_g⁺ (ν = 0,J) + 2hv → E,F¹Σ_g⁺(ν_E,J_E = J) + hν → H₂⁺X²Σ_g⁺ (ν⁺) + e^?, for ν_E = 0, 1, or 2 and for J_E = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν⁺ = ν_E, the detailed H₂⁺ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the J_E value of the intermediate state and the ν⁺ value of the ion.