J. T. Moseley

Photofragment spectroscopy and potential curves of Ar+2

Photofragment energy distributions have been measured for the process Ar+2(2Σ+u)+hν→Ar++Ar using a 3 keV ion beam and cw lasers both coaxial and crossed with the ion beam, polarized, respectively, perpendicular and parallel to the ion beam direction. Measurements were made at 14 wavelengths between 4579 and 7993 A. Transitions to the dissociative states 2Πg and 2Σ+g are observed, as are the effects of the spin–orbit interaction in Ar+2. The experimental results are used along with theoretical calculations to determine the 2Σ+u, 2Σ+g, and 2Πg potentials. The effects of the spin–orbit interaction on the potential curves, the magnitude and wavelength dependence of the photodissociation cross section, and the angular distributions of the photofragments are considered.

Ion–Ion Recombination Total Cross Sections—Atomic Species

A multistate Landau–Zener method is set up for the calculation of atomic ion–ion mutual neutralization total cross sections. The results of the calculations are compared with experimental results for O++O−, N++O−, He++D−, He++H−, and H++H−. The energy range scanned depends on the system but varies between about 0.1 and 10 000 eV. The agreement between theory and experiment is usually within a factor of 2.

Photodissociation and photodetachment of molecular negative ions. III. Ions formed in CO2/O2/H2O mixtures

Total photodestruction cross sections for O2−, O3−, O4−, O2−⋅H2O, CO4−, CO3−, and CO3−⋅H2O have been measured over the range from 6950 to 4579 A (1.78–2.71 eV). In most cases the photodestruction of these ions can be attributed to specific photodissociation or photodetachment processes. The ions HCO3− and HCO3−⋅H2O have also been investigated, and upper limits determined for their total photodestruction. The experiments were performed using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The cross section values vary from 2×10−20 to 1×10−17 cm2, and in most cases photodissociation is the predominant process. In CO3− and O3− evidence is found for bound, predissociating excited states.

Photodissociation Spectroscopy of CO3(

The photodissociation cross section of gas‐phase CO3 − has been measured over the wavelength range from 4579 to 6940 A, and reveals detailed structure reflecting the vibrational spacings of a predissociating excited electronic state. From an analysis of the structure, we identified three vibrational modes of the excited state having energies of 990, 1470, and 880 cm−1. The bond energy D (CO2–O−) of the ground state CO3− was determined to be 1.8±0.1 eV, and the electron affinity of CO3 was found to be 2.9±0.3 eV. By comparison with theoretical calculations, the lowest predissociating state was identified as 1 2A1. Observations regarding other excited states of CO3− are made.

Photodissociation and photodetachment of molecular negative ions. II. Ions formed in oxygen

Total photodestruction cross sections for O−2, O−3, and O−4 ions have been measured over a photon energy range of 1.93–2.71 eV using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The O−2 ion is found to photodetach at these photon energies with a cross section which varies from 1.2 to 2.2×10−18 cm2. The O−3 ion photodissociates to form O− over this energy range with a cross section which varies from 0.1 to 7.3×10−18 cm2 and exhibits structure indicative of the vibrational levels of a predissociating excited state. Structure is also observed in the O−4 photodestruction cross section which varies from 1.0 to 2.2×10−18 cm2, and in the O−2 photodetachment cross section.

Photodissociation and Photodetachment of Molecular Negative Ions. I. Ions Formed in CO2/H2O Mixtures.

A drift tube mass spectrometer and an argon ion laser have been used to study photon interactions with CO−3, CO−3⋅H2O, HCO−3, and HCO−3⋅H2O at discrete photon energies between 2.35 and 2.71 eV. CO−3 photodissociates into CO2+O− with a cross section which varies between 0.3 and 1.0×10−18 cm2 over this energy range. CO−3⋅H2O photodissociates into CO−3+H2O with a cross section near 2×10−18 cm2. HCO−3 and HCO−3⋅H2O have very small (and possibly zero) cross sections for photodestruction on this energy range.

Predissociation lifetimes of the rotational and fine structure levels of O2+(b4Σ−g, v=3,4,5)

A fast ion beam coaxial with a single mode laser has been used to measure the absorption linewidths of predissociated levels of O+2(b4Σg−, v=3,4,5) by detection of the O+ photofragments. Tuning of the absorption wavelength was accomplished by a combination of intracavity etalons and variation of the ion beam velocity (Doppler tuning). Lifetimes were determined for the b state fine structure levels of rotational levels N=31 and 33 of 16O2+(v=3), N=9–25 of 16O2+(v=4), N=14–27 of 16,18O2+(v=4), and N=5–7 of 16O2+(v=5). The lifetimes vary from 0.06 to 4 nsec. Variation with all relevant quantum numbers and with isotopic composition is discussed.

Photodissociation of atmospheric positive ions. I. 5300–6700 Å

Photodissociation cross sections have been investigated for several positive ions of atmospheric importance in the wavelength region from 5300 to 6700 A, using a drift tube mass spectrometer and a tunable dye laser. The dimer ions NONO+ and CO2CO+2 are observed to have large photodissociation cross sections (≳10−17 cm2) at these wavelengths. Three ions formed from oxygen cations O+4, CO+4, and O+2⋅H2O have photodissociation cross sections near 1×10−18 cm2, with the latter two ions exhibiting a threshold near 6200 A. The cluster ions NO+⋅M, where M is H2O, N2, CO2, and N2O, are not observed to photodissociate, nor are H3O+⋅ (H2O)n=0,1,2. Upper limits on the photodissociation cross sections for these ions are established in the range 10−19–10−20 cm2. For many of the ions studied here reactions coupling the ion of interest with other species present in the drift tube and diffusion effects following interaction with the laser must be explicitly considered to establish values or limits for the photodissociatio...

Photodissociation and photodetachment of Cl2−,ClO−, Cl3− and BrCl2−

Absolute cross sections for the photodestruction of Cl2−, ClO−, Cl3−, and BrCl2− were measured over the wavelength range of 3500–7600 A using a drift tube mass spectrometer–laser apparatus. The photodissociation cross section for Cl2− has two bands, as has been observed for the isoelectronic Ar2+ ion. The wavelength dependence of these bands is used to adjust the calculated potential curves of the ion in the Franck–Condon region. The photodestruction cross section for ClO− has a narrow band peaked at 4300 A with a width of 400 A, superimposed on a continuum that slowly increases with photon energy. The narrow band is attributed to photodissociation and the continuum to photodetachment. Cl3− and BrCl2− have no significiant photodestruction cross sections for wavelengths longer than 4700 A. At shorter wavelengths, the cross sections increase with increasing photon energy. The photodestruction of these ions is attributed to photodissociation. The present gas phase measurements are compared with optical spect...

Time‐of‐flight determination of lifetimes of N2+(A 2Πu)‐the Meinel band system

Radiative lifetimes of N2+(A 2Πu ) have been determined for vibrational levels v′=1−8. They decrease monotonically from 13.9± 1.0 μ sec for ν′=1 to 7.3 ± 0.5 μ sec for v′=8. A time‐of‐flight method was used to overcome collisional and diffusion effects that have affected most other measurements.