We present a combined experimental and theoretical investigation of the electronic spectra of barbituric acid (BA) and 2-thiobarbituric acid (TBA) molecules in the vapour phase. The valence band photoemission and the core level (O, N, C 1s and S 2p) photoemission and photoabsorption spectra have been measured in the vapour phase using synchrotron light and then assigned with the support of quantum chemical calculations. First the valence band binding energies have been calculated using the Koopman's approximation at the B3LYP/6- 311++G** level, then the outer valence behaviour has been better approximated with electron propagator calculations (OVGF and P3 approximations), available in the G09 software package. [1] The core ionized states and core-to-excited states transitions were solved within the Hartree-Fock approximation by explicitly taking into account the core hole, using the GSCF3 code developed by prof. N. Kosugi. [2] The calculations were run for both the tri-keto and the hydroxy-di-keto form, where the enolization of one of the two equivalent keto groups is produced by proton transfer from the methylene group, which is more acidic than the NH groups. In agreement with previous ab initio [3, 4] and gas-phase electron diffraction [5] works, only the tri-keto tautomers have been detected. [1] Gaussian 09, Revision A.02, M. J. Frisch et al., Gaussian, Inc., Wallingford CT, 2009. [2] N. Kosugi, and H. Kuroda, Chem. Phys. Lett. 74, 1980, 490. N. Kosugi, and H. Kuroda, Chem. Phys. Lett., 94, 1983, 377. N. Kosugi, Theor. Chim. Acta, 72, 1987, 149. [3] F. Zuccarello, G. Buemi, C. Gandolfo and A. Contino, Spectrochim Acta A, 59, 2003, 139-151. [4] E. Méndez, M. F. Cerdá, J. S. Gancheff, J. Torres, C. Kremer, J. Castiglioni, M. Kieninger, and O. N. Ventura, J. Phys. Chem. C, 111, 2007, 3369-3383 [5] O. V. Dorofeeva, I. I. Marochkin, N. M. Karasev, I. F. Shishkov and H. Oberhammer, Structural Chemistry, 22, 2011, 419-425
A. Maris, S. Melandri, L. Evangelisti, V. Feyer, K. C. Prince, M. Coreno (2011). Soft X-ray photoelectron-photoabsorption spectroscopy and electronic structure of barbituric and 2-thiobarbituric acid.. s.l : s.n.
Soft X-ray photoelectron-photoabsorption spectroscopy and electronic structure of barbituric and 2-thiobarbituric acid.
MARIS, ASSIMO;MELANDRI, SONIA;EVANGELISTI, LUCA;
2011
Abstract
We present a combined experimental and theoretical investigation of the electronic spectra of barbituric acid (BA) and 2-thiobarbituric acid (TBA) molecules in the vapour phase. The valence band photoemission and the core level (O, N, C 1s and S 2p) photoemission and photoabsorption spectra have been measured in the vapour phase using synchrotron light and then assigned with the support of quantum chemical calculations. First the valence band binding energies have been calculated using the Koopman's approximation at the B3LYP/6- 311++G** level, then the outer valence behaviour has been better approximated with electron propagator calculations (OVGF and P3 approximations), available in the G09 software package. [1] The core ionized states and core-to-excited states transitions were solved within the Hartree-Fock approximation by explicitly taking into account the core hole, using the GSCF3 code developed by prof. N. Kosugi. [2] The calculations were run for both the tri-keto and the hydroxy-di-keto form, where the enolization of one of the two equivalent keto groups is produced by proton transfer from the methylene group, which is more acidic than the NH groups. In agreement with previous ab initio [3, 4] and gas-phase electron diffraction [5] works, only the tri-keto tautomers have been detected. [1] Gaussian 09, Revision A.02, M. J. Frisch et al., Gaussian, Inc., Wallingford CT, 2009. [2] N. Kosugi, and H. Kuroda, Chem. Phys. Lett. 74, 1980, 490. N. Kosugi, and H. Kuroda, Chem. Phys. Lett., 94, 1983, 377. N. Kosugi, Theor. Chim. Acta, 72, 1987, 149. [3] F. Zuccarello, G. Buemi, C. Gandolfo and A. Contino, Spectrochim Acta A, 59, 2003, 139-151. [4] E. Méndez, M. F. Cerdá, J. S. Gancheff, J. Torres, C. Kremer, J. Castiglioni, M. Kieninger, and O. N. Ventura, J. Phys. Chem. C, 111, 2007, 3369-3383 [5] O. V. Dorofeeva, I. I. Marochkin, N. M. Karasev, I. F. Shishkov and H. Oberhammer, Structural Chemistry, 22, 2011, 419-425I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
