Mark L. Polak

Ultraviolet photoelectron spectroscopy of the phenide, benzyl and phenoxide anions, with ab initio calculations

Abstract The 351 nm photoelectron spectra of the phenide, benzyl and phenoxide anions are reported. Information obtained for phenyl radical includes an adiabatic electron affinity (EA) of 1.096(6) eV, two vibrational modes at 600(10) and 968(15) cm −1 , and an excited electronic state at ⩽ 1.7 eV. For benzyl, the radical EA is 0.912(6)eV, a vibration appears at 514(15)cm −1 , and another is possibly present at 1510(25)cm −1 . Phenoxyl radical has an EA of 2.253(6)eV, exhibits a vibration at 515(15) cm −1 , and possibly another at 1490(25) cm −1 . The first excited state of phenoxyl radical appears at 1.06(5) eV above the ground state. Ab initio calculations using GAUSSIAN 88 are used to elicit geometries, normal modes of the active vibrations, and help confirm the presence of various vibrations. Combining our results with previous measurements we find gas-phase acidities for benzene and toluene of 399(2) kcal mol −1 and 380.5(1.5) kcal mol −1 respectively, and a hydrogen bond dissociation energy for phenol of 86.5(2)kcal mol −1 .

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.

Photoelectron spectroscopy of the halogen oxide anions FO−, ClO−, BrO−, IO−, OClO−, and OIO−

The 351 nm photoelectron spectra of FO−, ClO−, BrO−, IO−, OClO−, and OIO− are reported. The spectra of the halogen monoxides display transitions to both spin–orbit states of the 2Πi ground state neutrals. Anion vibrational frequencies are observed in the spectra and bond lengths are obtained for the anions from Franck–Condon simulations. Spectra of the halogen dioxides display two active vibrational modes—the symmetric stretch and the bend. Anion symmetric stretching frequencies and normal coordinate displacements from the corresponding neutral are reported. Adiabatic electron affinities found for the halogen oxides are 2.272(6) eV (FO), 2.276(6) eV (ClO), 2.353(6) eV (BrO), 2.378(6) eV (IO), 2.140(8) eV (OClO), and 2.577(8) eV (OIO). The difference between the neutral and anion dissociation energies [D0(XO)−D0(XO−)] is reported for each of the halogen monoxides. Anion heats of formation (298 K) are also determined.

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...

A study of the structure and dynamics of the hydronium ion by high resolution infrared laser spectroscopy. II. The ν4 perpendicular bending mode of H3 16O

Sixty‐six lines in the ν4 band of H3O+ have been measured using diode laser velocity modulation spectroscopy. 36 have been assigned to the a–a component of the spectrum and 30 to the s–s component. The observed spectra were fit to a standard symmetric top Hamiltonian including the effects of l‐type doubling. The band origin of the s–s transitions is at 1625.947(5) cm−1, whereas that of the a–a component lies at 1638.533(3) cm−1. The effect of the asymmetric bending vibration on the inversion splitting is in qualitative agreement with previous theoretical results, but the experimental band origins deviate by about 60 cm−1 from calculated values. Coriolis perturbations are found to have an important effect on the rotational constants of the ν4 and ν2 levels.

Absolute infrared vibrational band intensities of molecular ions determined by direct laser absorption spectroscopy in fast ion beams

The technique of direct laser absorption spectroscopy in fast ion beams has been employed for the determination of absolute integrated band intensities (S0v) for the ν3 fundamental bands of H3O+ and NH+4. In addition, the absolute band intensities for the ν1 fundamental bands of HN+2 and HCO+ have been remeasured. The values obtained in units of cm−2 atm−1 at STP are 1880(290) and 580(90) for the ν1 fundamentals of HN+2 and HCO+, respectively; and 4000(800) and 1220(190) for the ν3 fundamentals of H3O+ and NH+4, respectively. Comparisons with ab initio results are presented.

Passive Fourier-transform infrared spectroscopy of chemical plumes: an algorithm for quantitative interpretation and real-time background removal

We present a ratioing algorithm for quantitative analysis of the passive Fourier-transform infrared spectrum of a chemical plume. We show that the transmission of a near-field plume is given by τ(plume) = (L(obsd) - L(bb-plume))/(L(bkgd) - L(bb-plume)), where τ(plume) is the frequency-dependent transmission of the plume, L(obsd) is the spectral radiance of the scene that contains the plume, L(bkgd) is the spectral radiance of the same scene without the plume, and L(bb-plume) is the spectral radiance of a blackbody at the plume temperature. The algorithm simultaneously achieves background removal, elimination of the spectrometer internal signature, and quantification of the plume spectral transmission. It has applications to both real-time processing for plume visualization and quantitative measurements of plume column densities. The plume temperature (L(bb-plume)), which is not always precisely known, can have a profound effect on the quantitative interpretation of the algorithm and is discussed in detail. Finally, we provide an illustrative example of the use of the algorithm on a trichloroethylene and acetone plume.

Photoelectron spectroscopy of negatively charged bismuth clusters: Bi−2, Bi−3, and Bi−4

We have recorded the 351 nm photoelectron spectra of Bi−2, Bi−3, and Bi−4. The spectrum of Bi−2 shows transitions to at least seven electronic states of Bi2 neutral, four of which are observed with vibrational resolution. Term energies, bond lengths, and vibrational frequencies are obtained for the anion ground state and for the first three excited states of Bi2. These results are compared to previous spectroscopic measurements and to the ab initio calculations presented in the accompanying paper. The photoelectron spectrum of Bi−3 reveals some of the electronic structure of Bi3 and the results are discussed in comparison to recent theoretical work. Adiabatic electron affinities are obtained for Bi2 [1.271(8) eV] and for Bi3 [1.60(3) eV]. The electron affinity of Bi4 is estimated from the onset of photodetachment to be 1.05(10) eV.

Determination of the Born–Oppenheimer potential function of CCl+ by velocity modulation diode laser spectroscopy

Over 70 transitions among the lowest six vibrational states of C35Cl+ and C37Cl+ have been measured between 1070–1210 cm^−1. The spectrum has been fitted to a sixth order Dunham expansion to yield an accurate mapping of the Born–Oppenheimer potential function of CCl+. The spectroscopic constants obtained are ωe = 1177.7196(8) cm^−1, ωexe = 6.6475(3) cm^−1, and Be = 0.797 940(3) cm^−1. The rotational constants for both CCl+ isotopes reported here show the results of the previous electronic emission studies to be incorrect. A fit of the data to a Morse function yields a dissociation energy D of 52 828(50) cm^−1. The rotational temperature has been determined as 540 K±30%. The increase in the effective vibrational temperature with vibrational excitation indicates that CCl+ is formed with high internal energy.

Photoelectron spectroscopy of group IV heavy metal dimers: Sn−2, Pb−2, and SnPb−

Negative ion photoelectron spectra of Sn−2, SnPb−, and Pb−2 are presented for electron binding energies up to 3.35 eV. Each spectrum exhibits multiple electronic bands, most of which contain resolved vibrational structure. Franck‐Condon analyses yield spectroscopic parameters (re, ωe, and Te) for the anion ground states and the neutral excited states. Adiabatic electron affinities are determined to be: EA(Sn2)=1.962±0.010 eV, EA(Pb2)=1.366±0.010 eV, and EA(SnPb)=1.569±0.008 eV. The anion dissociation energies D0(Sn−2) and D0(Pb−2) are derived from the electron affinities and the neutral dissociation energies. For SnPb−, the dissociation energy difference D0(SnPb−)−D0(SnPb) is precisely measured. Based on the present data, previous experiments and ab initio calculations, we assign most of the observed bands to the corresponding neutral low‐lying electronic states.