Determination of the CO3- bond strength via the resonant two-photon photodissociation threshold:: Electronic and vibrational spectroscopy of CO3-•Arn

We use a two-laser pump-probe technique coupled with messenger atom tagging to determine the bond energy of O- to CO2 in the CO3- ion, a prevalent species in the upper atmosphere. In this technique, the argon-tagged ion is first electronically excited using a visible laser, then irradiated with a tunable near-infrared beam across the CO2 center dot center dot center dot O- dissociation threshold while O- products are monitored. This method yields a bond energy of 2.79 +/- 0.05 eV, which is about 0.5 eV higher than previously reported. Combining this with the well-known heats of formation of O- and CO2, 105.6 and -393.1 kJ/mol, respectively [Thermodynamic Properties of Individual Substances, edited by L. V. Gurvich, I. V. Veyts, and C. B. Alcock (Hemisphere, New York, 1989), Vol. 1 and CODATA Thermodynamic Tables, edited by O. Garvin, V. B. Parker, and J. H. J. White (Hemisphere, New York, 1987)], yields the CO3- heat of formation: Delta H-0(0)=-556.7 +/- 4.8 kJ/mol. The one-photon (i.e., linear) infrared and electronic spectra of CO3- are also presented and compared to those obtained previously. The one-photon electronic spectrum is nearly identical to two-photon spectra, implying that argon does not significantly perturb the ion or its symmetry. The infrared spectrum is drastically different than that obtained in an argon matrix, however, indicating that the ion is likely distorted in the matrix environment. (c) 2006 American Institute of Physics.