P. C. Engelking

Laser photodetachment electron spectrometry of methoxide, deuteromethoxide, and thiomethoxide: Electron affinities and vibrational structure of CH30, CD30, and CH3S

Photodetachment of the three anions CH3O−, CD3O−, and CH3S− by a fixed‐frequency argon ion laser at 488 nm and subsequent energy analysis of the photoelectrons yields the photoelectron spectra of these species. From the spectra, electron affinities were determined: E.A.(CH3O) = (1.570±0.022) eV, E.A.(CD3O) = (1.552±0.022) eV, E.A.(CH3S) = (1.882±0.024) eV. From the vibrational structure appearing in the spectra, and the shifts observed upon deuteration, the predominant motion excited in the neutral upon photodetachment of CH3O− and CD3O− is found to be the symmetric hydrogen umbrella bend at 1325±30 and 1010±30 cm−1, respectively. In CH3S both the symmetric hydrogen bend and the carbon–sulfur bond stretch (680±40 cm−1) are excited. From the observed hot bands, some vibrational frequencies of the negative ions are also derived.

Laser photoelectron, photodetachment, and photodestruction spectra of O−3

Fixed frequency laser photoelectron spectrometry and variable frequency laser photodetachment and photodestruction spectroscopy of the ozonide ion, O−3, have been accomplished. The electron affinity of ozone is measured to be EA(O3) =2.1028(25) eV, in good agreement with previous measurements of less accuracy. Progressions in the spectra are analyzed to yield the symmetric stretching frequency and the bending frequency of the ozonide ion to be 982(30) and 550(50) cm−1, respectively. While no evidence is found for a long lived excited electronic state of O−3, an excited electronic state of neutral ozone is found roughly 0.7–1.1 eV above the ground state. Models for the dissociation of O3− are examined to explain why the photoelectron and photodetachment spectra fail to show a strong progression in the symmetric bending vibrational mode. Attempts to measure the electron affinity of CO−3 were unsuccessful. Limits placed by this attempt and our EA(O3) value are invoked in a discussion of some recent disagreem...

Photoinduced evaporation of charged clusters

The average cluster size remaining after photoinduced evaporation of a cluster of specific initial size can be predicted by an RRK/QET statistical model, provided that the correct average kinetic energy release is used. Theoretical justification for this correction, based upon detailed balance, is provided here. Agreement with experiments on (CO2)+ n clusters at several wavelengths shows that for these aggregates the average bond strength above n=2 is approximately 3.6±0.6 kcal/mol.

Laser photoelectron spectrometry of C5H−5: A determination of the electron affinity and Jahn–Teller coupling in cyclopentadienyl

The photodetachment electron spectrum of cyclopentadienide (C5H−5) yields a value for the cyclopentadienyl electron affinity of 1.786±0.020 eV. Additionally, the spectrum shows structure corresponding to vibrations in the neutral radical. From this an upper bound is placed on the linear Jahn–Teller coupling constant k2<0.5. The quadratic coupling is shown theoretically to be absent for this molecule, a special case of the absence of quadratic coupling in Dn or Cn groups when n is not divisible by three. The magnitude of this Jahn–Teller distortion is sufficient to induce nontotally symmetric Jahn–Teller modes in the spectrum, but is insufficient to suppress the symmetric modes and, in particular, a strong 0–0 transition is observed. Thus, the geometries of the ion and the neutral, apart from the Jahn–Teller distortion, are not radically different.

Laser photoelectron spectrometry of FeO−: Electron affinity, electronic state separations, and ground state vibrations of iron oxide, and a new ground state assignment

The photoelectron spectrum of FeO− ions, obtained with 2.54 eV Arii irradiation, consists of a well resolved series of vibrational transitions from the ground electronic state of the negative ion to two low‐lying electronic states of FeO. Analysis of this spectrum gives the electron affinity of FeO (1.492±0.020 eV) and the vibrational frequency of the negative ion (740±60 cm−1). The vibrational frequency of the ground state of FeO is 970±60 cm−1; the term energy T0 of the first excited state of FeO is 3990±100 cm−1. The FeO vibrational frequency shows definitively that the accepted ordering of FeO states is incorrect, and that the previously assumed ground state must in fact be an excited state. Earlier spectroscopic studies of FeO are re‐examined, and a new state ordering, consistent with all experimental data, is proposed.

Laser photoelectron spectroscopy of CH2−, and the singlet–triplet splitting in methylene

Photodetachment of an electron from CH2− ions using visible light produces CH2 in both its ground 3B1 and lowest excited 1A1 states. In an earlier letter, this process was utilized to determine directly a singlet–triplet splitting of 19.5 kcal/mol. In this paper are reported the details of the early measurement and a number of additional investigations designed to test critically the earlier assignments. Data reported here indicate that one suggested problem with the early results, a misassignment of the 3B1 origin resulting from negative ion hot bands, is not likely. These new results do reveal the presence of an additional peak in the photoelectron spectrum which could possibly be the lowest level of the 3B1 state, allowing a singlet–triplet splitting of 19.5 or 23.2 kcal/mol. The results reported here do not indicate any other inconsistency in the original assignment. Finally, these data are discussed in light of the formidable body of theoretical and indirect thermochemical determinations suggesting a...

Laser photoelectron spectrometry of Co− and Ni−

The photoelectron spectra of the negative ions Co− and Ni− have been obtained with a fixed frequency cw ArII laser (488 nm). The electron affinity of cobalt is found to be 0.662±0.010 eV, while that of nickel is 1.157±0.010 eV, in excellent agreement with a previously reported value E.A.(Ni) =1.15±0.15 eV determined by threshold photodetachment. Resolution of both negative ion and neutral fine structure intervals is obtained, and results in the determination of Co−: 3F4−3F3=910±50 cm−1, 3F3−3F2=650±50 cm−1 and Ni−: 2D5/2−2D3/2=1470±100 cm−1. The intensities of individual fine structure components are calculated from an angular momentum analysis of the photodetachment process and are compared with the experimental results. The fine structure intensities do not follow the (2J″+1) (2J′+1) statistical weighting of the negative ion (J″) and neutral (J′) spin–orbit states, but are much better represented by geometrical factors. The detachment of s electrons is preferred to the detachment of d electrons at 488 nm.

Laser photoelectron spectrometry measurement of characteristic electronic and vibrational temperatures of sputtered negative ions

The techniques of laser photoelectron spectrometry are used to characterize directly the internal energy distribution of sputtered negative ions. Effective temperatures of Telec≈1500±500 K and Tvib ≈5000±1000 K are determined. The excited electronic and vibrational state populations are not in equilibrium, in contrast to predictions of the local thermodynamic equilibrium model of sputtering.

LASER PHOTOELECTRON SPECTROMETRY OF THE NEGATIVE IONS OF IRON AND IRON CARBONYLS. ELECTRON AFFINITY DETERMINATION FOR THE SERIES FE(CO)N, N = 0,1,2,3,4

With a fixed-frequency Ar ion laser, the photoelectron spectra of the negative ions Fe-, FeCO-, Fe(CO)r-, Fe- (CO)3-, and Fe(C0)4- have been obtained. The electron affinity of iron is found to be (0.164 & 0.035) eV while the electron affinities for other members of this series increase roughly as the number of ligands. Thus for FeCO the EA is (1.26 f 0.02) eV; for Fe(C0)2, (I.22 f 0.02) eV; for Fe(CO)3, (1.8 f 0.2) eV; for Fe(C0)4, (2.4 & 0.3) eV. In addition, the photoelectron spectra provide information on vibration frequencies, electronic states, and Fe-CO bond strengths in these compounds.