Theoretical Study of the Electronic Gas-Phase Spectrum of Glycine, Alanine, and Related Amines and Carboxylic Acids

pi*(CO)) and the first Rydberg excitation from the nonbonding lone-pair on the nitrogen atom (n(N) --> 3s). From extensive calculations on formic acid and methylamine, different basis sets and electron correlation treatments are benchmarked using a hierarchy of coupled cluster (CC) methods, consisting of CCS, CC2, CCSD, CCSDR(3), and CC3, in combination with augmented correlation consistent basis sets. The dependence of the excitation energies on the size of the backbone structure in the two groups of molecules is investigated, and 0-0 transition energies for the n(O) --> pi*(CO) and n(N) --> 3s transitions are calculated for the smallest molecules. Excellent agreement with experimental values is found where secure experimental assignments are available. A few outstanding problems in the experimental assignments found in the literature are described for both the carboxylic acids and the amines. Final predictions for vertical excitation energies are given for all molecules, including glycine and alanine where no gas-phase experimental results are available. Finally, calculations on protonated amino acids are presented showing an isolation of the n(O) --> pi*(CO) from higher lying states by as much as 1.9 eV for alanine. -->
ISSN: 1520-5215
1089-5639
DOI: 10.1021/jp045697f
Přístupová URL adresa: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::256a3383524f2951fa6595653f83f04c
https://doi.org/10.1021/jp045697f
Rights: RESTRICTED
Přírůstkové číslo: edsair.doi.dedup.....256a3383524f2951fa6595653f83f04c
Autor: Ove Christiansen, Anders Osted, Jacob Kongsted
Rok vydání: 2005
Předmět:
Zdroj: Osted, A, Kongsted, J & Christiansen, O 2005, ' Theoretical study of the electronic gas-phase spectrum of glycine, alanine, and related amines and carboxylic acids ', Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, vol. 109, pp. 1430-1440 .
ISSN: 1520-5215
1089-5639
DOI: 10.1021/jp045697f
Popis: A theoretical study on the origin of the common electronic excitations in amino acids is presented, focusing on the excited states of glycine, alanine and the related substructures formic acid, acetic acid, propionic acid, ammonia, methylamine, and ethylamine. Special attention is given to the valence excitation from the nonbonding lone-pair on the carboxylic oxygen atom to the antibonding pi-orbital (n(O) --> pi*(CO)) and the first Rydberg excitation from the nonbonding lone-pair on the nitrogen atom (n(N) --> 3s). From extensive calculations on formic acid and methylamine, different basis sets and electron correlation treatments are benchmarked using a hierarchy of coupled cluster (CC) methods, consisting of CCS, CC2, CCSD, CCSDR(3), and CC3, in combination with augmented correlation consistent basis sets. The dependence of the excitation energies on the size of the backbone structure in the two groups of molecules is investigated, and 0-0 transition energies for the n(O) --> pi*(CO) and n(N) --> 3s transitions are calculated for the smallest molecules. Excellent agreement with experimental values is found where secure experimental assignments are available. A few outstanding problems in the experimental assignments found in the literature are described for both the carboxylic acids and the amines. Final predictions for vertical excitation energies are given for all molecules, including glycine and alanine where no gas-phase experimental results are available. Finally, calculations on protonated amino acids are presented showing an isolation of the n(O) --> pi*(CO) from higher lying states by as much as 1.9 eV for alanine.
Databáze: OpenAIRE
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