Amy E. Stevens Miller

Methylene: A study of the X̃ 3B1 and ã 1A1 states by photoelectron spectroscopy of C2H− and CD2−

Photoelectron spectra are reported for the CH2(X 3B1)+e−←CH−2 (X 2B1) and CH2(a 1A1)+e−←CH−2 (X 2B1) transitions of the methylene and perdeuterated methylene anions, using a new flowing afterglow photoelectron spectrometer with improved energy resolution (11 meV). Rotational relaxation of the ions to ∼300 K and partial vibrational relaxation to <1000 K in the flowing afterglow negative ion source reveal richly structured photoelectron spectra. Detailed rotational band contour analyses yield an electron affinity of 0.652±0.006 eV and a singlet–triplet splitting of 9.00±0.09 kcal/mol for CH2. (See also the following paper by Bunker and Sears.) For CD2, results give an electron affinity of 0.645±0.006 eV and a singlet–triplet splitting of 8.98±0.09 kcal/mol. Deuterium shifts suggest a zero point vibrational contribution of 0.27±0.40 kcal/mol to the observed singlet–triplet splitting, implying a Te value of 8.7±0.5 kcal/mol. Vibrational and partially resolved rotational structure is observed up to ∼9000 c...

Laser photoelectron spectroscopy of CrH−, CoH−, and NiH−: Periodic trends in the electronic structure of the transition-metal hydrides

The laser photoelectron spectra of CrH−, CoH−, and NiH− and the analogous deuterides are reported. The spectra are interpreted using a qualitative description of the electronic structure for the hydrides. This model is used to assign off‐diagonal transitions in the photodetachment to low‐spin states of the neutrals, and diagonal transitions to high‐spin states of the neutrals. These data are used to identify the high‐spin states of CoH and NiH; several other states of CrH, CoH, and NiH are also identified. Periodic trends in the bond lengths, vibrational frequencies, and electronic excitation energies for the MnH through NiH molecules are examined. Electron affinities are reported for CrH (0.563±0.010 eV), CoH (0.671±0.010 eV), and NiH (0.481±0.007 eV), and the corresponding deuterides.

Laser photoelectron spectroscopy of MnH−2, FeH−2, CoH−2, and NiH−2: Determination of the electron affinities for the metal dihydrides

The laser photoelectron spectra of MnH−2, FeH−2, CoH−2, and NiH−2 and the analogous deuterides are reported. Lack of vibrational structure in the spectra suggests that all of the dihydrides and their negative ions have linear geometries, and that the transitions observed in the spectra are due to the loss of nonbonding d electrons. The electron affinities for the metal dihydrides are determined to be 0.444±0.016 eV for MnH2, 1.049±0.014 eV for FeH2, 1.450±0.014 eV for CoH2, and 1.934±0.008 eV for NiH2. Electronic excitation energies are provided for excited states of FeH2, CoH2, and NiH2. Electron affinities and electronic excitation energies for the dideuterides are also reported. A limit on the electron affinity of CrH2 of ≥2.5 eV is determined. The electron affinities of the dihydrides directly correlate with the electron affinities of the high‐spin states of the monohydrides, and with the electron affinities of the metal atoms. These results are in agreement with a qualitative model developed for bond...

Original ArticlesMethyl bonding to Fe and Fe(CO)n:: reactions of Fe− and Fe(CO)n− with methyl halides2

Abstract Rate constants for atomic iron anion and successively ligated anions Fe(CO) n − (n = 0–4) reacting with CH 3 X (X = F, Cl, Br, I) were measured using a selected-ion flow tube apparatus. The results indicate that X − formation occurs as the dominant channel when exothermic. Other observed reaction channels are ligand exchange (with CH 3 and X replacing two CO), halogen-atom abstraction and adduct formation. Fe(CO) 4 − is too stable for a reaction with CH 3 X to develop by any channel. Fe(CO) 2 − displays a rich chemistry. Information on the bond strengths, D [Fe(CO) n CH 3 ], is deduced from the results. Under the assumption that the X − product channel is observed if exothermic, we calculate the homolytic iron–methyl bond energies 0.13 eV ≤ D [FeCH 3 ] ≤ 1.76 eV, D [Fe(CO)CH 3 ] = 1.2 ± 0.2 eV, D [Fe(CO) 2 CH 3 ] = 1.3 ± 0.3 eV, D [Fe(CO) 3 CH 3 ] D [Fe(CO) 4 CH 3 ]

Dissociative Electron Attachment to Transition-Metal Hydrides

A dissociation process is the terminal step for most electron recombination and electron attachment events, a commonality well illustrated by Prof. Fabrikant’s talk at this workshop. We have been studying dissociative electron attachment to extremely strong acid molecules. A distinguishing feature of these reactions is that a hydrogen atom may be thrown off from an acid AH upon electron attachment:

Acidity of a Nucleotide Base: Uracil

{e^ - }\left( {zero - energy} \right) + AH - >{A^ - } + H

Gas-phase acidities of pentacarbonyl manganese, iron, and cobalt hydrides, (CO)5MnH, (CO)4FeH2, and (CO)4CoH

(1) provided that the gas-phase acidity of AH is less than 13.6 eV. (The gas phase acidity is the bond energy D[H+ -A-]; an acidity < 13.6 eV denotes an extremely strong acid - termed a gas phase superacid). The first study of electron attachment to gas-phase superacids was that of Adams et al.,1 who found rapid attachment to common superacids such as fluorosulfonic acid. Adams et al. speculated that the large attachment rate coefficients observed were a consequence of the extreme acidity of the target molecules they studied.