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Notes: The vibrational state distributions of N+2(X˜,v') ions resulting from the reactions, Ar+(2P3/2)+N2(X˜,v=0)→Ar(1S0) +N+2(X˜,v') [reaction (1)] and Ar+(2P1/2)+N2(X˜,v=0)→Ar(1S0) +N+2(X˜,v') [reaction (2)], over the center-of-mass collisional energy (Ec.m.) range of 0.25–41.2 eV in a crossed ion–neutral beam experiment have been probed by the charge exchange method. The experimental results obtained for reaction (1) are in accord with the predictions of the semiclassical multistate calculation of Spalburg and Gislason that N+2 ions are formed predominantly ((approximately-greater-than)85%) in the v'=1 state and that the production of N+2(X˜,v'=0) becomes more important as Ec.m. is increased. The experiment also supports the theoretical results for reaction (2) at Ec.m.=1.2 and 4.1 eV showing that (approximately-greater-than)80% of N+2 product ions are in the v'=2 state. However, the calculation is found to either over-estimate the populations for N+2(v'〈2) or underestimate the populations for N+2(v'〉2) resulting from reaction (2) at Ec.m.=10.3and 41.2 eV. Absolute spin-orbit-state-selected total cross sections for reactions (1) and (2), σ3/2 and σ1/2, respectively, at the Ec.m. range of 0.25–115.3 eV have also been measured using a tandem photoionization mass spectrometer which is equipped with a radio frequency (RF) octopole ion guide reaction gas cell. The measured values for σ3/2 at Ec.m.=4.1, 10.3, and 41.2 eV and σ1/2 at 41.2 eV are in reasonable agreement with the theoretical cross sections. However, the experimental values for σ3/2 at 1.2 eV and σ1/2 at 1.2, 4.1, and 10.3 eV are approximately a factor of 2 higher than the theoretical predictions. A model analysis, which takes into account possible collision-induced spin-orbit mixings of the reactant Ar+ states in the RF octopole gas cell, shows that the values for σ1/2/σ3/2 and σ1/2 determined using the ion beam–RF octopole gas cell arrangement can be strongly susceptible to gas cell pressure effects whereas the experimental values for σ3/2 are reliable. The values for σ1/2 deduced by multiplying the values for σ3/2 and the ratios σ1/2/σ3/2 determined in the crossed ion–neutral beam experiment are in agreement with the theoretical cross sections. Both σ3/2 and σ1/2 are found to increase as Ec.m. is increased from 41.2 eV. This observation is interpreted as due to the formation of N+2 in the A˜ 2Πu state at high Ec.m. . Combining the measured vibrational state distributions of product N+2(X˜,v') ions and the absolute state-selected total cross sections, absolute state-to-state total cross sections for reactions (1) and (2) at selected Ec.m. are determined.

Notes: Photoionization efficiency data for HgKr+ and HgXe+ have been obtained in the region of 730–1290 A(ring). The ionization energies (IE) of HgKr and HgXe are determined to be 10.056±0.012 (1233±1.5 A(ring)) and 9.709±0.011 eV (1277±1.5 A(ring)), respectively. Using these values, the known dissociation energies of HgKr and HgXe, and the IE of Hg, the binding energies for the ground-state mercury-rare gas molecular ions are calculated to be 0.393±0.013 eV for HgKr+ and 0.748±0.013 eV for HgXe+. By analyzing the shifts in energy between corresponding autoionization peaks observed in the Kr+, HgKr+, Xe+, and HgXe+ spectra and by assuming the charge induced-dipole interaction to be the dominant interaction at the equilibrium bond distances for HgKr and HgXe, the equilibrium bond distances for HgKr and HgXe are deduced to be 3.98 and 4.23 A(ring), respectively. The latter values are in excellent agreement with values determined by previous spectroscopic studies.

Notes: Higher resolution photoionization efficiency data for the formation of S+2 and S+ from S2 in the wavelength region of 600–1350 A(ring) have been obtained using the supersonic oven beam method. The ionization energy (IE) of S2 is determined to be 9.356±0.002 eV (1325.2±0.3 A(ring)). The measured appearance energy of 14.732±0.005 eV (841.6±0.3 A(ring)) for the dissociative ionization process S2+hν→S++S+e−, together with the IE of S2, yields a value of 5.376±0.005 eV for the bond dissociation energy of S+2. Two Rydberg series converging to the b˜ 4Σ−g state (13.20 eV) of S+2 are observed. Window resonances resolved in the wavelength region of 670–850 A(ring) are assigned as members of the Rydberg series converging to the c˜ 4Σ−u (17.70 eV) and 2Πu (or 2Σ−u) (18.66 eV) states of S+2.

Notes: Relative vibrational-state-selected total cross sections σv', v'=0–2, for the reaction N+2(X˜,v'=0–2)+Ar(1S0)→N2(X,v +Ar+(2P3/2,1/2) [reaction (1)], over the center-of-mass collisional energy (Ec.m.) range of 1.2–320 eV have been determined using the crossed ion–neutral beam photoionization apparatus. The experimental results at Ec.m.=1.2–40 eV are in agreement with those obtained in previous experimental and theoretical studies, indicating that σ0 is substantially less than σ1 and σ2. As Ec.m. is increased, σ0 becomes comparable to σ1 and σ2 in the Ec.m. range of ∼140–200 eV. At Ec.m.=260 and 320 eV, the cross sections are in the order σ0〉σ1〉σ2. The fractions of Ar+(2P1/2) resulting from reaction (1), Xv'→1/2, v'=0–2, at Ec.m.=4–320 eV have been measured by the charge exchange method. The measurement shows that the Ar+ product ions are predominantly((approximately-greater-than)80%) formed in the 2P3/2 state, an observation qualitatively in accord with the predictions of semiclassical multistate calculations. The predicted values for Xv'→1/2, v'=0–2, at Ec.m.=8, 20, and 40 eV are higher than the experimental values. The values for X0→1/2 at Ec.m.=8–320 eV and X1→1/2 at Ec.m.=4–40 eV are found to increase as Ec.m. is increased, showing the behavior of an endothermic process. The values for X1→1/2 and X2→1/2 remain approximately constant at the the Ec.m. ranges of 40–320 and 8–200 eV, respectively. The measured relative state-to-state cross sections for reaction (1) and the reaction Ar+(2P3/2,1/2)+N2(X,v=0)→Ar(1S0) +N+2(X˜,v') are consistent from the consideration of microscopic reversibility.

Notes: A new ion–molecule rection apparatus, which consists of a photoionization source, a tandem mass spectrometer, and a radio frequency octopole reaction cell is described. Using a quadrupole mass filter to reject H+3 background ions formed at the photoionization source, absolute total cross sections for the reaction H+2 (v'0) +H2 (v'0 =0)→H+3 +H, have been measured as a function of the vibrational state of reactant H+2, where v'0 =0–4, over the center-of-mass collision energy (Ec.m.) range of 0.04–15 eV. The experimental results are compared with phenomenological cross sections obtained in previous single gas cell studies, the quasiclassical trajectory calculations of Stine and Muckerman, and the recent similar calculations of Eaker and Schatz. The absolute total cross sections measured for v0 =0 and 3 at Ec.m. =0.5, 1, 3, and 5 eV are found to be in agreement with "trajectory surface hopping'' calculations which include nonadiabatic surface hopping throughout the reaction.

Notes: The relative spin-orbit-state-selected total charge transfer cross sections, σ3/2 and σ1/2, for the reactions, Ar+ (2P3/2,1/2)+N2 (X˜ 1∑+g ,v=0) → Ar+N+2 at the center-of-mass collision energy (Ec.m.) range of 0.41–164.7 eV, have been determined using the photoionization and crossed ion–neutral beam methods. The kinetic energy dependences for σ1/2/σ3/2 is found to exhibit a minimum at Ec.m.≈3.3 eV, an observation consistent with the prediction of a recent semiclassical theoretical calculation of Spalburg and Gislason.

Notes: The vibrational state distributions of product H+2(v‘) resulting from the symmetric charge transfer reactions H+2(v'0=0 or 1) +H2(v‘0=0) →H2(v') +H+2(v‘) in the center-of-mass collisional energy (Ec.m.) range of 2–16 eV have been measured by the charge exchange method. When reactant H+2 ions are prepared in v'0 =0, the majority (〉80%) of product H+2 ions are formed in v‘=0. The vibrational relaxation channel for forming H+2(v‘=0) is found to be much more efficient than the vibrational excitation process for producing H+2(v‘=2) in the H+2(v0=1) +H2(v‘0=0) charge transfer collisions. The experiment also reveals that inelastic charge transfer channels become more important as Ec.m. is increased. The vibrational state distributions of product H+2(v‘) determined at Ec.m. =8 and 16 eV are compared with results of the semiclassical energy conserving trajectory calculations of Lee and DePristo. A better agreement between experimental and theoretical results is observed at Ec.m. =16 eV, a collisional energy at which charge transfer is the overwhelming channel.