F. Howorka

Collisional relaxation of vibrationally excited NO+(v) ions

Vibrationally excited O2+ ions were produced and injected into a helium flow tube and found to survive more than 105 collisions with He atoms without significant relaxation. The first, second, and higher vibrational states of O2+ were detected by their enhanced reactions with Xe, SO2, and H2O. Using these reactions as probes for vibrational excitation, the relaxation of O2+ (v=1) and O2+ (v=2) ions was studied for collisions with Ne, Ar, Kr, H2, D2, N2, CO, CO2, H2O, CH4, SO2, SF6, and O2. The resulting quenching rate constants were found to vary from 1(−9) to <2(−15) cm3 s−1. The quenching rate constant of O2+ (v=2) was approximately twice that of O2+ (v=1) in each case. The rate constants were found to correlate with the bond energy of the ion–molecule collision complex. For CO2, Kr, and O2, the energy dependence of the quenching rate constant was investigated in the range 0.04–0.3 eV. The results indicate that the relaxation process proceeds through a long‐lived complex where the vibrational excitation...

Vibrational relaxation of NO+ (v) ions in neutral collisions

Vibrational relaxation of NO+ (v) by collisions with NO, N2, CO2, CH4, NO2, He, Ar, and Kr has b een measured from thermal energy up to 1 eV. NO+ (v) is vibrationally relaxed at near the collision frequency by resonant charge transfer with NO. N2 is quite efficient due to near resonant V → V transfer. CO2, CH4, and NO2 are efficient, Ar, Kr, and especially He are not. The quenching rate constants for N2, CO2, and CH4 decrease with KE, those for NO and NO2 do not.

Reaction rate constants in steady‐state hollow cathode discharges: N2 + H2O reactions

In a cylindrical hollow cathode discharge in N2 with traces of H2O, there is a distribution of ion types from the edge of the negative glow to the axis of the cylinder. This distribution was explored by using a small, radially movable probe with an entrance aperture to a mass spectrometer in the probe. Ions could then be extracted from the negative glow plasma from any desired radial location in the cylinder. The results show N2+ and N+ at the edge of the glow giving way to N2H+, H2O+, and H3O+ toward the axis. Clearly, ion‐molecule reactions are proceeding in the field‐free negative glow region. Quantitative rate constant measurements were obtained for formation and destruction of N2H+, H2+, N+, and the formation of H2O+ and H3O+. The measurements on N2+ and N+ formation by electron collisions give values for the density of high energy electrons in the negative glow. Adequate agreement is found with values obtained by other workers using other methods, where overlap occurs. The present new and different ...

The proton transfer from ArH+ to various neutrals

The proton transfer reactions from ArH+ to H2, D2, CH4, N2, O2, CO, CO2, and the corresponding deuteron transfer reaction of ArD+ with H2 and D2 have been investigated in a drift tube with mass selected ion injection. The use of helium and argon buffer gases permits a qualitative assessment of vibrational energy effects along with a quantitative assessment of the influence of translational energy on reaction rates. These exothermic reactions all proceed with large rate coefficients which approach the collision rates for the respective reactants. All except the reaction of ArH+ with H2 (D2) were independent of translational energy over the range investigated. In an argon buffer equilibrium is readily established for the reaction ArH++H2⇄H3++Ar. A treatment of the center‐of‐mass kinetic energy as a ’’translational temperature’’ permits the construction of a van’t Hoff plot for this reaction from which a value of Δ(PA)=0.55 eV is obtained, which is consistent with the accepted proton affinities of H2 and Ar.

Excitation cross sections in collisions of He+, Ne+, Ar+, N+, N+2, O+2, H+2, and H+3 ions with CF4

Excitation processes in the collisions of He+, Ne+, Ar+, N+, N+2, O+2, H+2, and H+3 with tetraflouromethane have been studied in the energy range 1–1800 eV laboratory frame and the wavelength region 2000–8000 A. Absolute cross sections dependent on energy are measured. Several excitation processes have been observed: Excitation of a continuous emission band and discrete emission bands, and excitation of atomic lines; neutral and ionic carbon and fluorine lines, X i and X ii lines (X+ being the primary ion), and excitation of the Balmer series in collisions of H+2 and H+3 with CF4. The recombination energy of the incident ion seems to play a dominant role for the excitation of molecular emissions, whereas the kinetic energy seems to be responsible for the excitation of atomic lines.

Noble gas halide ions: KrCl+, KrF+, ArCl+, ArI+

Noble gas halide ions are observed mass spectrometrically in low‐pressure discharges of noble gas halide mixtures like Kr+Cl2 and Ar+Cl2. Under similar discharge conditions, KrCl+ forms more readily than ArCl+. The most probable process of producing KrCl+ is three‐body association of Kr to Cl+ with an estimated rate coefficient of 4×10−28cm6s−1. ArCl+ cannot be formed in this way because the recombination energy of Cl+ is too low by ≳1 eV. KrF+ is observed weakly in Kr+CF4 or Kr+SF6 mixtures. ArI+ can only be observed when Ar+I2 mixtures are traversed by accelerated electrons and the ArI+ ions are not allowed to collide with neutrals or electrons. A negative peak of mass number 59 observed in Ar+CF4 could be ArF−, but is probably an impurity like C2OF−.

Energy dependences of reactive and quenching collisions of N2+(X,v > o) with O2 and NO.

Abstract A fast flow drift tube with mass selected ion injection system was used to investigate the energy dependences of reactive and quenching collisions of N 2 + (X,v > o) with O 2 and NO in the energy range from thermal to 2 eV relative kinetic energy between the reactants, KE cm . The rate coefficients for the charge transfer show the same energy dependences as the respective rate coefficients for the charge transfer of N 2 + (X, v = o) with O 2 and NO. The rate coefficient for the quenching of N 2 + (X, v > o) to N 2 (X, v = o) is k q = 1 × 10 −10 cm 3 sec −1 and nearly independent of KE cm in the case of O 2 . In the case of NO, k q increases from k q −11 cm 3 sec −1 at thermal energy to k q ∼ 1.5 × 10 −10 cm 3 sec −1 at a few tenths of an eV.

Cylindrical hollow cathode as a source of negative ions

Abstract The negative-ion density distribution across the negative glow of a hollow cathode discharge in O2 shows a sharp maximum near the sheath edge where the ions are trapped in a shallow potential well. The hollow cathode is found to be well suited as a negative-ion source when the ions are extracted from this region near the sheath edge. Both O− and O2− ions have been studied to date. The mechanisms of their production are discussed.

Excited state formation in the interaction of mass resolved ion beams with molecular and atomic targets (1 – 4000 eV, 200 – 800 nm)

Abstract A 60° magnetic mass spectrometer is used to inject singly and doubly charged ion beams of up to 250 nA current and 1 – 4000 eV energy into a chamber which is filled with atomic or molecular gas (0 – 1 Pa). The light produced by the interaction processes is analyzed in a 0.5 m monochromator and the photons are counted in a cooled multiplier - single photon counting arrangement. From the light-to-ion current ratio, a total cross section for excitation is defined and its energy dependence is measured. The measured curves are explained in terms of a multiple-crossing Landau-Zener-Stuckelberg approach.