Negative ion photoelectron spectroscopy NIPES

In negative ion photoelectron spectroscopy (NIPES), the reactant is a negative ion, and the upper state is neutral. In this case, the origin can be used to determine the electron affinity. 

Ion cyclotron resonance (ICR) and flowing afterglow experiments can also be used to derive relative affinities. Neutral beam experiments, where a beam of alkali atoms such as Cs is crossed with a beam of molecules such as PCI3 or (012)2 have been used to derive thermochemistry for anions such as PCli" and Cli", but proper analysis of this type of data is difficult. High-resolution negative ion photoelectron spectroscopy (NIPES) experiments can provide otherwise unobtainable information on hypervalent anions, including precise electron affinities and vibrational frequencies.This technique has limited applicability to hypervalent species with more than three atoms because of vibrational congestion from low-frequency modes. 

To overcome this problem we recently suggested to correlate the ionization potential (IP) and the electron affinities (EA) of carbenes with the carbene philicity. [14] IP and EA of carbenes can in principle be measured by negative ion photoelectron spectroscopy (NIPES), and data of a series of simple carbenes and vinylidenes were published by Lineberger et al. [15-23] The experimental data allow to evaluate the reliability of theoretical methods for the calculation of IP and EA. As shown in Table 1, there is a decent agreement between the experimental EA and calculations of the vertical EA of carbenes. The calculated adiabatic EAs are systematically too large by ca. 0.3 eV. However, if the adiabatic EAs are corrected by this value the agreement with the experiment is even better. 

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