THE HIDDEN FACET OF THE C-3-PI STATE OF SO

Reliable evidence is presented which shows that the (CII)-I-3 state of SO, previously thought to be mostly repulsive, does in fact have a re latively deep potential. As a result of an avoided crossing around 3.9 a(0), this state does have, for large internuclear distances, the rep ulsive nature experimentalists have agreed upon, and which has somehow been incorrectly extended to shorter distances; its supposed repulsiv e nature may have discouraged theoreticians from exploring excited sta tes other than A (3) Pi, B-3 Sigma(-), and (3) Delta. As a consequence of the findings of this work, all existing experimental data on the e xcited states of B (3) Sigma(-) and part of A(3) Pi will necessarily h ave to be reanalysed to properly take into account the perturbations c aused by these new 3 Pi states and other lower lying (3) Sigma(+) and 3 Delta states on the spectra of SO. The theoretical predictions of th is work were based on a state averaged complete active space self-cons istent/internally contracted multireference configuration interaction (CASSCF/CMRCI) calculation using averaged natural orbitals expanded in terms of the cc-pVQZ set of atomic functions. The following spectrosc opic constants characterizing these new states have been found: R-e = 3.177 a(0), T-e = 5.46 eV, Delta G(nu + 1/2) = 704, 681, 655, 634, 616 , 607 and 622 cm(-1) (nu = 0-6), omega(e) = 747 cm(-1), omega(e)x(e) = 21.06 cm(-1), omega(e)y(e) = 1.114 cm(-1), R-max = 3.914 a(0), E-max= 0.64eV for what we now call the C-3 Pi; and R-e=3.883 a(0), T-e=6.15 e V, Delta G(nu+1/2) = 817, 752, 641 and 152 cm(-1) (nu = 0-3), omega(e) = 838 cm(-1) omega(e)x(e) = -2.04 cm(-1), omega(e)y(e) = -7.702 cm(-1 ), R-max = 4.394 a(0), E-max = 0.42 eV, for what we now call the C'(3) Pi state. The very anharmonic nature of the latter state is obviously manifested in the vibrational constants.