CCL:G: electron affinity
- From: Karl Irikura <karl.irikura]-[nist.gov>
- Subject: CCL:G: electron affinity
- Date: Wed, 08 Nov 2006 08:54:05 -0500
Sent to CCL by: Karl Irikura [karl.irikura-x-nist.gov]
Hi. In the chemistry WebBook (http://webbook.nist.gov/chemistry/)
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.
Regards,
Karl
At 07:39 AM 11/8/2006, you wrote:
Sent to CCL by: "Dr. Ponnadurai Ramasami" [ramchemi-#-intnet.mu]
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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.
Ramasami
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Dr. Karl K. Irikura
National Institute of Standards and Technology
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