Photodetachment of negative ions

By comparing the chemical shifts and peak heights of an unknown with standards or known reference materials, some predictions of the unknown structure can be made. In some exceptional but important cases, such as the photodetachment of negative ions, the wavelength of light causing photoionization is in the visible or even the near infrared, allowing extremely precise structure determinations. 

Although the abovementioned theories were formulated in the context of either photoionization of atoms or electron scattering with atoms, they lend themselves equally well to photodetachment of negative ions, where an essential question is again to construct the wavefunction for the total continuum state in the presence of transient states embedded in continua. The main results from Mies s work [54] for calculating cross sections are summarized below. 

Anion photoelectron spectroscopy [37, 38] amd photodetachment techniques [39] provide accurate information on electron detachment energies of negative ions. Ten closed-shell ainions considered here exhibit sharp peaks, indicative of minor or vanishing final-state nuclear rearrangements, in their photoelectron spectra. Comparisons between theory and experiment are straiightforward, for differences between vertical and adiabatic electron detachment energies (VEDEs and AEDEs, respectively) are small. 

J.L. Sanz-Vicario, E. Lindroth, N. Brandefelt, Photodetachment of negative helium ions below and above the Is ionization threshold A complex scaled configuration-interaction approach, Phys. Rev. A 66 (2002) 052713. 

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. 

Anion photoelectron spectroscopy is conducted by crossing a mass-selected beam of negative ions with a fixed-frequency photon beam and energy-analyzing the resultant photodetached electrons (Figure 21-8). There are three main regions of such an apparatus the source that generates the anions to be studied, the mass... 

Many-body theory has also been applied to calculate the response of negative ions [253], where intershell interactions and core rearrangement effects are even greater than for neutral atoms. It turns out that the spectra of photodetachment in negative ions are dominated by correlation effects to an even greater degree than photoionisation for neutral atoms. 

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

The above fomuilae for the absorption spectrum can be applied, with minor modifications, to other one-photon spectroscopies, for example, emission spectroscopy, photoionization spectroscopy and photodetachment spectroscopy (photoionization of a negative ion). For stimulated emission spectroscopy, the factor of fflj is simply replaced by cOg, the stimulated light frequency however, for spontaneous emission... 

The transition-state spectroscopy experiment based on negative-ion photodetachment described above is well suited to the study of the F + FI2 reaction. The experiment is carried out tln-ough measurement of the photoelectron spectrum of the anion FH,. This species is calculated to be stable with a binding energy of... 

Kitsopoulos T N, Chick C J, Zhao Y and Neumark D M 1991 Study of the low-lying electronic states of Sij and Si. using negative ion photodetachment techniques J. Chem. Phys. 95 1441... 

Photodetachment/Photoionization Photodetachment and photoionization refer to the processes of removing an electron from either a negative ion or a neutral molecule. 

An important feature of photodetachment methods is that the selection rule for electronic transition is A5 = +1. Therefore, photodetachment of (doublet) negative ions... 

---