CCL:G: electron affinity

 Sent to CCL by: Karl Irikura []
Hi. In the chemistry WebBook ( the EA is listed as 1.3261 eV (or 127.95 kJ/mol) but there is an annotation by John Bartmess (Univ. Tennessee) that G3(MP2) calculations predict the anion to be unbound by > 1.5 eV (> 140 kJ/mol). Your calculation also predicts the anion to be unbound. There is a paper by EPF Lee et al. [CPL 336(5-6) 479 (2001)] concluding that the anion is unstable. So your result appears qualitatively correct. The actual value you get will depend strongly upon the basis set. Try it! Add (in Gaussian, keyword is "extrabasis") a diffuse s-function with exponent of 0.0001 to the basis set on one of the atoms. The calculated EA should get close to zero; the diffuse function mimics a continuum function, allowing the added electron to avoid the molecule.
Electron affinity, as a thermodynamic quantity, must be non-negative (unless, arguably, a metastable anion is long-lived; see Lee's paper, or papers by L-S Wang about multiply charged anions). But sometimes resonances in electron scattering are loosely described as states of negative electron affinity.
 At 07:39 AM 11/8/2006, you wrote:
 Sent to CCL by: "Dr. Ponnadurai Ramasami" []
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 Dear All
 I am calculating the electron affinity of carbon monoxide using =
 B3LYP/aug-cc-pVTZ by evaluating E(CO, neutral) - E(CO, negative).
 I am getting a negative value of -100.2 kJ/mol.
 The literature experimental value is 127.9 kJ/mol (I guess positive).
 Is this correct?
 Can electron affinity be negative?
 I will appreciate in case someone can help.
 Dr. Karl K. Irikura
 National Institute of Standards and Technology
 100 Bureau Drive, Stop 8380
 Gaithersburg, MD  20899-8380
 voice: 301-975-2510     fax: 301-869-4020