Kent M. Ervin

Translational energy dependence of Ar++XY→ArX++Y (XY=H2,D2,HD) from thermal to 30 eV c.m.

Cross sections for the reactions of Ar+ with H2, D2, and HD to form ArH+ and ArD+ are measured using a new guided ion beam tandem mass spectrometer which affords an experimental energy range from 0.05 to 500 eV laboratory. The apparatus and experimental techniques are described in detail. Cross sections for H2 and D2 are found to be nearly identical over this entire energy range when compared at the same barycentric energy. The total HD cross section is the same as H2 and D2 at low energies, but differs significantly above 4 eVu2009c.m., where product dissociation becomes important. The intramolecular isotope effect for reaction with HD exhibits a reversal at low energy, favoring the deuteride product below ∼0.14 eVu2009c.m., and surprising nonmonotonic behavior at energies above 5 eVu2009c.m. In all these systems, a new feature at higher energies is observed. This is interpreted as the onset of a product channel having an energy barrier of 8±1 eV. The room temperature rate constant derived from the data for the reac...

A study of the singlet and triplet states of vinylidene by photoelectron spectroscopy of H2C=C−, D2C=C−, and HDC=C−. Vinylidene–acetylene isomerization

The Xu20091A1, au20093B2, and bu20093A2 states of vinylidene are observed in the ultraviolet (351.1–364.0 nm) photoelectron spectra of Xu20092B2 H2CC−, Xu20092B2 D2CC−, and Xu20092A’ HDCC−. The Xu20091A1 state exhibits vibrational structure well above the barrier for isomerization to acetylene. A strict lower bound to the lifetime of the singlet state against rearrangement is τ>0.027 ps, with an estimate of τ≊0.04–0.2 ps based on a simulation of the line shapes including rotational broadening. A vibrational analysis of the singlet and lower triplet state bands provides vibrational frequencies and estimates of the changes of molecular geometries between the anion and the neutral species. A qualitative potential energy surface for the CH2 rock mode, which closely corresponds to the reaction coordinate for isomerization, is extracted from the experimental data. The adiabatic electron affinity is EA(Xu20091A1 H2CC)=0.490±0.006 eV and the triplet term energies are T0(au20093B2 H2CC)=2.065±0.006 eV and T0(bu20093A2 H2CC)=2.754±0.020 eV. Exp...

Electronic and vibrational structure of transition metal trimers: Photoelectron spectra of Ni−3, Pd−3, and Pt−3

The transition metal trimer anions Ni−3, Pd−3, and Pt−3 are prepared in a flowing afterglow ion source with a cold cathode dc discharge. The low‐lying electronic states of the neutral trimers are probed by 488 nm negative ion photoelectron spectroscopy at an electron kinetic energy resolution of 5–12 meV. Each trimer exhibits multiple low‐lying electronic states. Vibrational progressions are observed in tripalladium and triplatinum. The adiabatic electron affinities are found to be EA(Ni3)=1.41±0.05 eV, EA(Pd3)≲1.5±0.1 eV, and EA (Pt3)=1.87±0.02 eV.

Photoelectron spectroscopy of nickel group dimers: Ni−2, Pd−2, and Pt−2

Negative ion photoelectron spectra of Ni−2, Pd−2, and Pt−2 are presented for electron binding energies up to 3.35 eV at an instrumental resolution of 8–10 meV. The metal cluster anions are prepared in a flowing afterglow ion source. Each dimer exhibits multiple low‐lying electronic states and a vibrationally resolved ground state transition. Franck–Condon analyses yield the anion and neutral vibrational frequencies and the bond length changes between anion and neutral. The electron affinities are determined to be EA(Ni2)=0.926±0.010 eV, EA(Pd2)=1.685±0.008 eV, and EA(Pt2)=1.898±0.008 eV. The electronic configurations of the ground states are tentatively assigned. Comparison of the nickel group dimers to the coinage metal dimers sheds light on the d orbital contribution to the metal bonding in the nickel group dimers.

Energy dependence, kinetic isotope effects, and thermochemistry of the nearly thermoneutral reactions N+(3P)+H2(HD,D2)→NH+(ND+)+H(D)

The reactions of N+(3P) ions with H2, HD, D2 are examined using guided ion beam tandem mass spectroscopy. Absolute reaction cross sections are measured from near thermal energies to 30 eV relative energy. The low energy cross section behavior is analyzed using empirical threshold models and phase space theory. The results are compared to other recent studies of the N++H2 system. The reaction endothermicity for N+(3P)+H2→NH++H, ΔH○0 =0.033±0.024 eV (0.76±0.55 kcal/mol), and the bond energy of NH+, D○0(N–H+) =3.51±0.03 eV (80.9±0.6 kcal/mol), are derived from the results.

Translational energy dependence of O+(4S) + H2(D2, HD) → OH+(OD+) + H(D) from thermal energies to 30 eV c.m.

Abstract Guided ion beam mass spectrometry is used to examine the kinetic energy dependences of the reactions of ground-state atomic oxygen ion with molecular hydrogen and its isotopic variants. At interaction energies below 0.3 eV, the total reaction cross-sections for all three systems are in excellent agreement with those predicted by the Langevin-Gioumousis-Stevenson model for exothermic ion/molecule reactions. At energies above 0.3 eV, the reaction efficiency declines. Phase space theory calculations are used to show that this behavior is due partly to angular momentum constraints. Above 6 eV, dissociation of the product ion is evident. For reaction with HD, the intramolecular isotope branching ratio oscillates several times over the energy range examined. This result is explained by comparison with phase space theory calculations and with several dynamical models.

C+(2P)+H2(D2,HD)→CH+(CD+)+H(D). I. Reaction cross sections and kinetic isotope effects from threshold to 15 eV c.m.

Total cross sections for the reactions of carbon(1+) ions with isotopic molecular hydrogen (H2, D2, and HD) to form methyliumylidene (CH+ and CD+) have been measured using guided ion beam techniques. Cross sections are reported as a function of the translational energy of the reactants from the reaction threshold up to 15 eV c.m. The true cross sections are shown to rise sharply from thresholds given by the thermochemical endothermicities. Inter‐ and intramolecular isotope effects in the threshold region can be attributed to the different endothermicities due to vibrational zero‐point energies. At higher energies, an unexpected intermolecular isotope effect is found. Thermal reaction rates (300 K) derived from the data are 1.2×10−16 for H2, 2.3×10−17 for D2, and 1.2×10−16 for HD (17% CH+, 83% CD+), all in units of cm3u2009s−1.

A study of the electronic structures of Pd2- and Pd2 by photoelectron spectroscopy

The ultraviolet negative ion photoelectron spectrum of Pd−2 is presented for electron binding energies up to 3.35 eV. The anion is prepared by sputtering in a flowing afterglow ion source. Multiple low‐lying electronic states of Pd2, all unidentified previously, are observed with resolved vibrational structure. The spectrum shows two strong electronic bands, each with similar vibrational progressions. Franck–Condon analyses are carried out on the two transitions and molecular constants are extracted for the anion and the two neutral electronic states. With the help of simple molecular orbital arguments and ab initio calculations, these two electronic bands are assigned as the triplet ground state (3Σ+u) and a singlet excited state (1Σ+u). The adiabatic electron affinity is E.A.(Pd2)=1.685±0.008 eV and the singlet excitation energy T0(1Σ+u) is 0.497±0.008 eV (4008±65 cm−1 ). The bonding in the palladium dimers is discussed and we find that the anion bond strength is 1.123±0.013 eV stronger than that of the...

Translational energy dependence of O+(4S)+N2→NO++N from thermal energies to 30 eV c.m.

Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of the reaction of ground state atomic oxygen ion with molecular nitrogen. An O+(4S) source which produces less than 0.06% excited states is described. Cross sections for the NO++N product channel decrease with increasing energy below 0.25 eV but increase with energy at higher energies. Analysis of the region above 0.25 eV finds an effective barrier of 0.33±0.08 eV which previous theoretical work suggests is on the N2O+(1u20094A‘) hypersurface. Below this barrier, ground state products can only be formed via a spin‐forbidden surface transition. The magnitude and energy dependence of the probability for this transition are in reasonable agreement with a Landau–Zener formalism. These results are compared to previous ion beam, flowing afterglow (FA), and flow/drift tube (FD) studies. Apparent disagreement between the present data and previous FA and FD measurement is shown to be caused primarily by differences in the ion energy di...

NH2 electron affinity

The 363.8 nm (3.408 eV) photoelectron spectrum of the NH2 (Xu20092B1)+e−←NH−2(Xu20091A1) transition of the amide anion is reported. The electron affinity of amidogen is found to be EA(NH2) =0.771 ±0.005 eV. P, Q, and R rotational branches are observed in the spectrum; a simple model which accounts for the band structure is presented.