L. Serranoandres et al., INTERPRETATION OF THE ELECTRONIC ABSORPTION-SPECTRUM OF FREE-BASE PORPHIN BY USING MULTICONFIGURATIONAL 2ND-ORDER PERTURBATION-THEORY, Chemical physics letters, 295(3), 1998, pp. 195-203
Multiconfigurational second-order perturbation (CASPT2) calculations h
ave been performed on the low-lying optically allowed valence excited
states of the free base porphin molecule in order to assign the four l
owest bands of the spectrum. The low-lying triplet states have also be
en characterized. A basis set of the atomic natural orbital type of sp
lit-valence plus polarization quality for first-row atoms has been emp
loyed. Polarization functions are important for an accurate descriptio
n of the transitions. These CASPT2 results provide a consistent pictur
e of the experimental spectrum. Each band of the spectrum up to 4.5 eV
is composed of a pair of states, which become degenerate in the spect
ra of metal-porphyrins. Our interpretation deviates from assignments b
ased on other types of ab initio calculations. (C) 1998 Elsevier Scien
ce B.V. All rights reserved.