Resonance electron photodetachment

The electron affinities listed in the table below agree within the error limits given. They were obtained by laser photoelectron spectroscopy (LPES) on the PHg ion [19] and PH2 photodetachment using a tunable laser (LPD) [20, 21] or an Xe arc lamp (with a grating monochromator) [21] and ion cyclotron resonance (ICR) spectrometry [20, 21]. All values are reported in two reviews on electron affinities [22] and electron photodetachment [23], and may be considered as adiabatic (see the remarks below the table) ... 

In order to study the viscosity effect on the quenching of triplet excited state of (53) by TEMPO, chemically induced dynamic electron polarization and transient absorption spectra have been measured in ethylene glycol, 1,2-propanol and their mixtures. The results indicate that the quenching rate constant is viscosity-dependent and decreases linearly with the increase in solvent viscosity. The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion have been studied using photoelectron imaging taken at 480 nm, which clearly indicates resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. ... 

Photoionization of neutral atoms and molecules and electron-ion collisions, for example, are rich in infinite Rydberg series of Feshbach resonances. On the other hand, only a finite number of Feshbach (and possibly shape) resonances occur in electron-neutral collisions and photodetachment of an electron attached to a neutral species, with an exception of the following cases. 

Photodetachment spectroscopy of negative ions like IHI- and similar systems, studied by Neumark and coworkers (Metz, Kitsopoulos, Weaver, and Neumark 1988 Weaver, Metz, Bradforth, and Neumark 1988 Metz et al. 1990 Bradforth et al. 1990 Neumark 1990 Weaver and Neumark 1991) has provided the first conclusive manifestation of reactive resonances for a purely repulsive PES. The idea of the experiment goes as follows a photon with frequency u detaches the electron from the negative ion producing e- and IHI. If the PES for the neutral molecule is dissociative, the IHI complex subsequently breaks apart into I and HI. 

Accurate measurements of the electron affinity of simple Ge and Sn radicals have been obtained by threshold photodetachment experiments carried out in ion cyclotron resonance experiments183. In these experiments, measurement of the threshold frequency for removing the electron from the anion yields an upper limit for the electron affinity of the species, as shown for GeH3- in equation 28. 

Following the above-mentioned spectroscopic study by Johnson and co-workers [55], Neumark and co-workers [56] explored the ultrafast real-time dynamics that occur after excitation into the CTTS precursor states of I (water) [n — 4-6) by applying a recently developed novel method with ultimate time resolution, i.e., femtosecond photoelectron spectroscopy (FPES). In anion FPES, a size-selected anion is electronically excited with a femtosecond laser pulse (the pump), and a second femtosecond laser pulse (the probe) induces photodetachment of the excess electron, the kinetic energy of which is determined. The time-ordered series of the resultant PE spectra represents the time evolution of the anion excited state projected on to the neutral ground state. In the study of 1 -(water), 263 nm (4.71 eV) and 790 nm (1.57 eV) pulses of 100 fs duration were used as pump and probe pulses, respectively. The pump pulse is resonant with the CTTS bands for all the clusters examined. 

We present the results of experimental studies of photon-negative ion interactions involving the dynamics of two electrons. Resonances associated with doubly excited states of Li and He" have been observed using laser photodetachment spectroscopy. Total and partial photodetachment cross sections have been investigated. In the former case, the residual atoms are detected irrespective of their excitation state, while in the latter case only those atoms in specific states are detected. This was achieved by the use of a state selective detection scheme based on the resonant ionization of the residual atoms. In addition, in the case of Li-photodetachment, the threshold behavior of the Li(2 P)+e-(ks) partial cross section has been used to accurately measure the electron affinity of Li. 

In Fig. 8 we show an extended 3 Skp partial photodetachment cross section which includes measurements below the LiCS S) threshold in addition to the data already shown in Fig. 7b. The data in the range 5.29-5.39 eV represents a relatively low statistics survey scan. It is normalized to the calculation of Pan et a/. [28] using the same factor as for the data between 5.39-5.46 eV. It is clear, even from this relatively low quality data, that the two resonances labeled f and g are observed at approximately the calculated energies but their measured strengths appear to be weaker than predicted. Presumably, the lowest lying resonance, labeled f, is the intrashell resonance representing symmetric excitation of the two valence electrons. 

Experimental evidence for the vibrational structure of XHX transition states has been provided by photoelectron spectroscopy of XHX- anions with X = Cl, Br, and I (134,160-163). This technique, by inducing photodetachment of an electron from the XHX" anions, probes the Franck-Condon region, which is believed for these systems to include geometries in the vicinity of the transition state region for the neutral systems. Spectral bands have been interpreted as evidence for trapped-state resonances associated with asymmetric stretch-excited levels of the transition state (160-163), and they are in general agreement with synthetic photoelectron spectra calculated from the scattering computations of Schatz (17-19). In recent experimental spectra (158,162), more closely spaced oscillations have been observed these are apparently related to rotational thresholds as described by Schatz. 

Rydberg states of Ba and Sr in an external magnetic field have been considered by Halley, Delande, and Taylor (35), by means of the R-matrix complex rotation method. Seipp and Taylor (36) used the same method for the Stark and Stark-Zeeman problem of Rydberg states of Na. Themelis and Nicolaides (96) investigated the ls 2s 2p 3s 5, 3p 4s 5, and 3d bound states of Na. They used the CESE method to compute tunneling rates and scalar and tensor polarizabilities and hyperpolarizabilities. Medikeri, Nair, and Mishra (145,146) considered shape resonances in Be", Mg" and Ca" in two-particle-one-hole-Tamm-Dancoff approximation. Photodetachment rate for Cl" described by one-electron model was computed by Yao and Chu (73)... 

The geometrical structure of gaseous PH2 in its X Ai ground state appears to be similar to that of ground-state PH2 (with an internuclear distance of r=1.42 A and an interbond angle of a = 92° see p. 72). This was inferred from a sharp increase of the photodetachment cross section at threshold, measured by ion cyclotron resonance [2, 3] and from the predominance of the (0, 0, 0)<-(0, 0, 0) transition in the PH2, X Bi PH, X A photoelectron spectrum [4]. r=1.34 0.05 A and a = 92 5 were taken from the isoelectronic H2S molecule (and used to calculate the thermodynamic functions of PH, see p. 109) [5]. r and a have also been theoretically calculated by several ab initio MO methods, i.e., at an MP2 [6, 7], a CEPA (coupled electron pair approximation) [8], and an HF level [9 to 15]. r was also obtained from a united-atom approximation [16] a was also calculated by a semiempirical (CNDO/2) method [17] and estimated by extended Huckel calculations [18]. 

The photodetachment signal, for example, shows a narrow Feshbach resonance at 10.93 eV—corresponding to an electron energy of 10.18 eV,... 

Brauman JI, Smith KC (1969) Photodetachment energies of negative ions by ion cyclotron resonance spectroscopy. Electron affinities of neutral radicals. J Am Chem Soc... 

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