Lifetime measurements of the excited states of N2 AND N2 by laser-induced fluorescence

Absorption and fluorescent scattering of nitrogen laser radiation by a low-pressure RF laboratory plasma (n_e = 10¹² cm⁻³) has been observed for the first negative system of N₂⁺. A 67±1 ns lifetime of N₂⁺ (B ²Σ_u⁺) was experimentally measured from the laser-induced fluorescence. In addition, enough collisionally excited N₂ (B ³Π_g) was produced to observe laser-induced fluorescence for the second positive system of N₂. The lifetime of N₂ (C ³Π_u) was found to be 41±2 ns. The measured lifetimes are in good agreement with published values calculated from theory.     

Deactivation of vibrationally excited N2 by H2O

The VV exchange rate for the N₂H₂O system is determined using a hard-core repulsive potential. It is found that the rapid deactivation rate arises from near-resonant VR exchanges involving non-dipole changes in the rotational states. Furthermore, a classical-path approximation is used and the resulting rate found to be critically dependent on the path chosen.     

Intermolecular forces for D2, N2, O2, F2 and CO2

The intermolecular potentials for D₂, N₂, O₂, F₂ and CO₂ are determined on the basis of the second virial coeffincients, the polarizabilities parallel and perpendicular to the molecular axes, and the electric quadrupole moment. The repulsive parts of the potentials are taken from the corresponding Kihara core-potentials. Effects of the octopolar induction are taken into consideration in a unique way. The potential depends on relative orientations of the two molecules as well as the distance r between the molecular centers. This dependence is shown in graphs. A measure of the anisotropy of the potential depth is 0.72 for CO₂ 0.36 for D₂, and smaller than 0.27 for N₂ O₂ and F₂. The remarkable anisotropy for CO₂ and D₂ is due to strong electrostatic quadrupole interactions.     

N2 laser pumped dye laser photolysis

An N₂ laser pumped dye laser has been used as the exciting pulse source in flash photolysis with a time resolution in the ns range. Using the apparatus described it was possible to monitor second order decays. Advantages of this set-up are tunability, reproducibility of the exciting source, and the rapidity of the measurements.     

Collisional ionization of alkali atoms by vibrationally excited N2

Chemiionization of alkali atoms by active nitrogen is studied in a crossed beam apparatus. Vibrationally excited N₂ in the electronic ground state is responsible for the ionization rather than electronically excited N₂ in the A ³∑_u⁺ state. The ionization cross section is of the order 10² A². The experimental data is consistent with the distribution of the vibrational levels of N₂ (X¹ ∑_g⁺) predicted by Bray or Caledonia and Center.     

High-resolution emission spectroscopy of CO2 collisionally excited by N2. Rotational distribution

We obtained, for the first time, high-resolution rotational distribution of CO₂ collisionally excited by N₂. The rotational distribution is non-Boltzmann, and the initial results suggest that surprisingly large impact parameter collisions contribute substantially to the collisional excitation, even though small impact parameter collisions are more effective, as expected.     

Laser excited fluorescence of I2

The fluorescence spectrum of iodine was investigated from 200 to 520 nm in the presence and absence of buffer gases following excitation of I₂ with 193 nm photons. The pressure dependence of the fluorescence and tentative transition assignments for one new and several less well-known I₂ emission bands are discussed.     

Isotope effects for the formation of slow and fast excited hydrogen atoms produced by controlled electron impact on H2 and D2

Analysis of the Balmer-β line taken at high resolution clarifies the isotope effect in the dissociative excitation of H₂. The isotope effect is larger for slow H¹ atoms (σ_D/σ_H = 0.4–0.6) than for fast H¹ atoms and has almost no electron energy dependence (25–100 eV).     

Two exponential decay of 3371 å laser excited CS2 fluorescence

We have observed time resolved CS₂ fluorescence excited by an N₂⁺ pulsed laser at 3371 Å. The optical absorption in this region is unassigned; we find two fluorescing states with collision free lifetimes of 2.9 ± 0.3 and 17 ± 2 μsec. Deactivation rates for both states are reported for the collision partners CS₂, Ar, O₂, and N₂. All rates are near gas kinetic; the 2.9 ± 0.3 μsec state exhibits exceptionally fast deactivation, with the rate constant for CS₂ being (7.9 ± 1.2) × 10⁻¹⁰ cm³/molecule sec.     

Kinetic study of gas-phase Lu(D3/2) with O2, N2O and CO2

The second-order rate constants of gas-phase Lu(²D_3/2) with O₂, N₂O and CO₂ from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule⁻¹ cm³ s⁻¹) are described in Arrhenius form by k(O₂)=(2.3±0.4)×10⁻¹⁰exp(−3.1±0.7 kJmol⁻¹/RT), k(N₂O)=(2.2±0.4)×10⁻¹⁰exp(−7.1±0.8 kJmol⁻¹/RT), k(CO₂)=(2.0±0.6)×10⁻¹⁰exp(−7.6±1.3 kJmol⁻¹/RT), where the uncertainties are ±2σ.     

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.     

Raman analysis of SF6 molecular beams excited by a cw CO2 laser

In a molecular beam the effects of vibrational pumping of SF₆ (ν₃ = 948 cm^?1) are studied, using a line-tunable cw CO₂ laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (x_E/D ≤ 1), a thermal redistribution of the ν₃ excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm^?1. For excitation in the relatively rare collision regime (x_E/D ? 4), a structured non-thermal ν₁ Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν₃ mode. The value of T_rot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν₃(948 cm^?1)+ΔE_rot → h(ν₄ + ν₆)(962 cm^?1) relative to the near-resonant transfer rate (hν₃ + hν₃ → 2hν₃ + 3.5 cm^?1)].     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Translational energy distribution of excited deuterium atoms produced by controlled electron impact on D2

The Balmer-β line of the excited deuterium atom [D*(n = 4)] produced in e—D₂ collisions has been measured at high resolution (0.029–0.033 Å) and at various electron energies (17–100 eV). The translational energy distribution of D*(n = 4) has been calculated from analysis of its Doppler line shape. The distribution of D* has three major components as in the case of H*(n = 4) from H₂ reported in our previous paper. Their peaks lie at about 0, 6 and 8 eV. The excitation function of D* is found to have two thresholds at 17.4 and 26.4 eV. The second component of D* has a larger translational energy and a higher threshold than those of the corresponding component of H*. These results indicate that the contribution from the lowest doubly excited state, ¹Σ_g⁺(2pσ_u)², is much smaller for D₂ than that for H₂.     

A CASSCF/icMRCI study of the electric field gradient in low-lying electronic states of N2/N2

The electric field gradients (EFG’s) at the nucleus are calculated as a function of internuclear separation in the X²Σ_g⁺ and B²Σ_u⁺ electronic states of the nitrogen molecule cation using the internally contracted multireference configuration interaction (icMRCI) method. The EFG’s and potential energy functions (PEF’s) are used to estimate the ¹⁴N nuclear quadrupole coupling constants (NQCC’s) in the two electronic states as functions of vibrational and end-over-end rotational quantum numbers. The dependences of the computed constants on the basis set and reference configuration space are investigated. Since no counterpart for comparison of the calculated NQCC’s exists, the N₂⁺ results are supported by analogous calculations on the X¹Σ_g⁺ and A³Σ_u⁺ states of N₂, for which established data are available. The overall good quality of the icMRCI wave functions is further corroborated by a favorable agreement of spectroscopic constants derived from the corresponding PEF’s and experimental data. Variations of the EFG with internuclear separation are explained in terms of wave function composition, and used for gaining specific insight into the chemical bonding in N₂⁺ and N₂.     

Vapour-liquid equilibrium data for the systems C2H6 + N2, C2H4 + N2, C3H8 + N2, and C3H6 + N2

High pressure vapour-liquid equilibrium data for the C₂H₆ + N₂, C₂H₄ + N₂, C₃H₈ + N₂, and C₃H₆ + N₂ systems are presented. The data are obtained isothermally in the range from 200 K to 290 K. For each point of data, temperature, pressure and liquid and vapour phase mole fractions are measured.Values for the vapour phase mole fractions are calculated from the obtained pressure, temperature and liquid phase mole fractions. The calculated values are compared with the experimental results, and it is found that the average mean deviation between calculated and experimental mole fractions is less than 0.009 for the systems considered in this work.     

Application of the N2 laser to laser microprobe spectrochemical analysis

Results are presented of a study on the application of a N₂ laser to the spectrochemical analysis of microareas. It is found that when the pressure of the surrounding gas is reduced to 1 Torr (133 Pa) or thereabouts, the plasma induced by the bombardment of N₂ laser light yields sharp atomic line spectra with a negligibly low background signal, facilitating quantitative analysis with reasonable precision. A simple and rapid detection method is employed in which the atomic emission spectrum from the plasma produced under successive bombardment (10 Hz) is recorded directly on a chart by means of scanning the wavelength of a monochromator. By using iron-steel standard samples of known content, it is demonstrated that a plot of the intensity of the 425.4 nm emission line of Cr against the Cr content shows a linear relationship.     

Time-resolved investigation of the de-excitation of xenon excimer by SF6 and N2 excited with synchrotron radiation

An attempt has been made 'o measure the rate constant for the de-excitation of a state-specified excimer using the pulse character of synchrotron radiation. The rate constants have been obtained for de-excitation of a vibrationally relaxed excimer Xe₂^*(O_u⁺; low v) by SF₆ and N₂ as 9 × 10^?10 and 7 × 10^?12 cm³ molecule^?1 s^?1 respectively.     

Experimental determination of the orientation of the molecular electric dipole moment within light molecules: A rotational zeeman effect study of H2CO and D2CO in excited vibrational states

It is known since long that at least in principle the orientation of the molecular electric dipole moment within a light molecule may be determined from the change of its molecular g-tensor elements upon isotopic substitution. In formaldehyde however, this method has lead to large discrepancies and has cast some doubts on its usefulness, at least as long as vibrational effects are neglected. The results of the present investigation indicate that vibrational effects are indeed responsible for the discrepancies and should be accounted for especially if hydrogen-deuterium substitutions are involved. In the appendix we discuss the problem to which approximation the same molecular property, called dipole moment, is measured by a rotational Stark effect experiment and by a rotational Zeeman effect experiment.     

Observation by laser ionization spectroscopy of vibrationally excited nitric oxide following O(1D2) + N2O → 2NO

Nitric oxide in ν < has been detected using one-proton resonant laser ionization spectroscopy following the reaction of electronically excited oxygen atoms with nitrous oxide. The nascent rotational distribution appears to differ significantly from that observed at 300 K.