William B. Maier

Study of the A → X Transitions in N2+ and CO+

Optical emissions from long‐lived, excited states of CO+ and N2+ in ion beams have been studied. CO or N2 is ionized by electron impact, and the ions are removed from the ion source to the observation region. Spectra of emission from CO+ and N2+ are obtained for wavelengths in the ranges 3200–5200 A and 6000–8700 A, respectively. All of the spectral features can be ascribed to the CO+ comet‐tail and N2+ Meinel emission systems. The electronic transition moments, Re, for these two emission systems are determined and are found to vary rather slowly with wavelength over the wavelength ranges for which we have data. Lifetimes of the v′=1, 2, 4, and 6 vibrational levels of CO+ (A 2π) are found to be 3.49, 2.78, 2.63, and 2.41 μsec, respectively. Lifetimes of the v′=2, 3, 4, and 5 vibrational levels of N2+(A2πu) are found to be 12.28, 10.70, 10.08, and 9.14 μsec, respectively. The dependences of the measured lifetimes on v′ are consistent with the experimental values of Re and with available Franck‐Condon fact...

Measurement and analysis of the infrared‐active stretching fundamental (ν3) of UF6

High‐resolution spectra of the infrared‐active stretching fundamental ν3 of 238UF6 have been obtained between 620.6 and 633.5 cm−1 using tunable semiconductor diode lasers. Interference from hot bands was suppressed by cooling the UF6 in a supersonic expansion, and useful monomer concentrations were produced with effective temperatures of <100 K. Portions of the band from P(77) to R(66) are illustrated. All transitions from the vibrational ground state have been assigned, and the Q branch has been fully analyzed. A total of 43 line frequencies and 110 frequency differences extending in J to P(77), Q(91), and R(67) has been used to fit seven spectroscopic constants. The ground‐ and excited‐state values of the rotational constant B could be individually determined, and the U–F bond length in the ground vibrational state is r0=1.9962±0.0007 A. The Q branch of 235UF6 has also been analyzed and the 235UF6–238UF6 ν3 isotope shift measured to be 0.603 79±0.000 17 cm−1. The isotope shift and the Coriolis constant...

Emission from Long‐Lived States in Ion Beams. New Band Systems of NO+

A method for investigating radiation from long‐lived, excited states of ions is described. Emission spectra, apparent lifetimes of the excited states, and electron impact cross sections for producing the radiation can be studied. The spectrum of emission from long‐lived states of NO+ in an ion beam has been obtained for wavelengths between 1250 and 2200 A, but no NO+ emissions have been observed in spectral scans of the 2200–3400‐A region. Some of the spectral features are produced by transitions to the X 1Σ+ state of NO+ from the υ′ = 0 and 1 levels of a single electronic state having an internuclear distance 1.157−0.01+0.02 A and an apparent lifetime 135 ± 35 μsec. These two vibrational levels are 7.301 ± 0.006 and 7.511 ± 0.01 eV above the ground state of NO+. The other emissions observed can be characterized by two apparent lifetimes, 10.8 ± 2 and 160 ± 50 μsec, and appear to be produced by transitions to the X 1Σ+ state from several upper states. Tentatively, the energies of the upper states are set ...

A lumped circuit model for transient arc discharges

Electrical breakdown of highly charged insulating systems can result in an arc discharge, i.e., a sudden, intense pulse of current. We model such arcs by a simple circuit: the discharge of a capacitor C (related to the initial charge reservoir) through a series inductor L and resistor R. For R=V*/‖Ia‖, where V* is a positive constant and Ia is the arc current, an essentially arbitrary dependence for L=L(Ia), a constant capacitance, and a circuit starting voltage V0, we establish four remarkable results for the subsequent arc discharge: (1) no discharge occurs at all unless ‖V0‖>V*; (2) if n is the largest non‐negative integer for which ‖V0‖≥(2n+1)V*, then the arc current will reverse sign precisely n times and will decline in amplitude by 2V* at each extreme; (3) the discharge stops abruptly at a final voltage Vf=(−1)n+1[V0−(n+1)2V* sgn V0]; (4) maxima and minima in Ia occur at voltages V=±V*. Results (1) and (3) provide the threshold condition and finite final potential necessary for any realistic arc di...

Production of Light by Collisions of 2.5–490 eV He+ with N2: NI, N2+ Second Negative, and Unresolved Emissions between 1200 and 3200 Å

The production of light in collisions between He+ and N2 has been studied at primary ion energies, E, between 2.5 and 490 eV. Strong emissions are present between 1200 and 3200 A, and spectra have been obtained for spectral resolutions between 1.5 and 16 A. NI emissions, N2+ second negative (2N) emissions, and strong, unresolved emissions have been found. The total cross section for producing the emission between 1200 and 3200 A is of the order of 10−16 cm2. For E < 40 eV, the cross section for producing the unresolved emissions is greater than the cross section for producing the N2+(2N) emissions. The cross section for production of the NI emissions decreases with decreasing E and vanishes near the threshold energies expected for NI emission produced by He++N2→N++N+He. With decreasing E, total cross sections for the N2+(2N) and unresolved emissions increase. Apparent populations of the vibrational levels of the N2+(2N) parent state depend differently on E; in particular, for E = 490 eV the υ′ = 1 and 2 ...

Reactions between H+ and D2

Cross sections have been measured for the production of D2+, HD+, and D+ in reactions between H+ and D2. The initial kinetic energies Ec.m. in the center‐of‐mass system are between 0.3 and 80 eV. The total cross section σT for these reactions can be represented by σT = 1.54 Ec.m.−0.7 for 8 ≤ Ec.m. ≤ 80 eV, and σT = 2.11 Ec.m.−1.43 for 0.3 ≤ Ec.m. ≤ 2 eV, where σT is in square angstroms, and Ec.m. is in electron volts. Apparent thresholds for the endothermic reactions H++D2→D2++H, H++D2→HD++D are found at Ec.m. = 1.84 ± 0.3 eV. The cross section for H++D2→D++HD drops rapidly with increasing energy. For Ec.m. ≳ 6 eV, D+ appears to be produced mostly by the reaction H++D2→D++D+H. When Ec.m. ≳ 8 eV, the reaction products are primarily D2+ and a smaller amount of D+. There is only fair agreement between these results and those of previous studies.

A theory of abrupt termination and spontaneous restart of electrical current in surface flashover arcs

The space‐time dynamics of surface flashover discharges is studied using a nonlinear one‐dimensional transmission line model. When the current I is not zero, the relation between the resistance per unit length, R, and I is assumed to be given by a local arc welder’s ansatz, R‖I‖=E*, where E* is a constant. The model predicts a threshold for discharge, and abrupt local termination and spontaneous restart of the discharge current. If at a place on the discharge path it happens that the charge gradient fails to exceed the threshold condition when the current vanishes, then the current will abruptly terminate there. However, if a discharge current flows in a region adjacent to one where the current has terminated, the edge of the current‐free region can be ‘‘ignited,’’ resulting in the ‘‘active’’ region encroaching on the ‘‘quiet’’ one. A formula for the speed of encroachment is derived. Formulas are also derived for current pulse waveforms and the charge transported during the discharge.

Visible and near ultraviolet light produced by the radiative decay of long‐lived states in a nitrogen ion beam

Optical emissions from the decay of long‐lived, excited states of 28N2+ and 30N2+ in ion beams have been studied. Spectra are obtained for wavelengths between 3200 and 6000 A. Most (∼ 80%−90%) of the emission is consistent with light emitted in A 2Πu → X 2Σg+ transitions, for A2Πu vibrational levels with ν′ as high as 30. For an electron energy Ee of 63 eV, about 25% of the 28N2+ produced is initially in the A2Πu, ν′ = 2–9 levels; 0.7% is in the ν′ = 10–19 levels; and 0.3% is in the ν′ = 20–30 levels. Energies of N2+ (A 2Πu, v′) states for ν′≤ 30 are found to be close to the energies calculated from formulas that are known to be valid when ν′ ≤ 9. The electronic transition moment Re is found to vary rather slowly for internuclear distances between 0.92 and 1.1 A. Apparent lifetimes of 6–7 μsec have been measured for emission in selected spectral ranges; these apparent lifetimes are consistent with the observed Re and with previously measured lifetimes of the A2Πu vibrational states. The electron energy ...

Study of Collisions between Low-Energy N+ and N2: Reaction Cross Sections, Isotopic Compositions, and Kinetic Energies of the Products

Reactive collisions between N+ and N2 have been studied, and cross sections for the production of N2+ have been measured for initial kinetic energies, Ec. m., in the center-of-mass system between 1 and 70 eV. The kinetic energies of the product N2+ have been determined. Isotopically labeled reactants were used, and the cross sections for producing N2+ containing different combinations of isotopes have been measured. The reaction N++N2→N2++N is found to proceed by both atom and electron transfer. For Ec. m. ≲ 11 eV, the cross sections for electron and atom transfer are roughly equal, but at higher Ec. m. the atom transfer cross section is considerably smaller than the electron transfer cross section. The kinetic energy −Q transferred into internal energy of the products is considerably larger than the minimum required for Reaction (1) to proceed. For the electron transfer process, the values determined for −Q are between 3 and 9.8 eV. The values of −Q found for the processes associated with atom transfer a...

Infrared absorption spectra of nitrogen oxides in liquid xenon. Isomerization of N2O3 a)

Infrared absorption spectra of nitrogen oxides present when NO and NO2 are dissolved in liquid xenon between 160 and 220 K have been measured. Spectral absorptions of NO, NO2, (NO)2, N2O4, and N2O3 are identified, and integrated absorption cross sections are given for several spectral features. The spectra suggest that symmetric N2O3 and asymmetric N2O3 are in equilibrium in solution and that the energy difference between these two isomers is 1.8±0.2 kcal/mol.