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Multireference singles and doubles configuration interaction calculations which include relativistic effective core potentials have been performed on GaAs. Potential energy curves of 40 Λ−S states are computed. Spectroscopic constants (T e , r e , and ω e ) of 17 bound Λ−S states have been estimated and compared with the available observed and other calculated values. The lowest Λ−S state is ...π2 X3Σ-. All 22 Λ −S states which dissociate into Ga(2P u ) + As(4S u ) and Ga(2P u ) + As(2D u ) limits are taken into consideration for the spin−orbit CI calculations. Potential energy curves of 51 Ω-states are computed. The X3 component is found to be the ground state of GaAs in contrary to the experimental findings which suggest the other component X3Σ1 - as the ground state. The splitting between the two components of X3Σ- is calculated to be 76 cm-1 as compared with the experimental value of 43 cm-1. The excited A3Π0 + state, which does not predissociate has r e = 2.757 Å, T e = 22 178 cm-1, and ω e = 125 cm-1. T e and ω e values are somewhat smaller, while r e is larger than the observed data. Transition probabilities of several dipole allowed transitions are calculated. Three transitions such as 1Σ+−41Σ+, 21Σ+−41Σ+, and X3Σ-−A3Π are found to be very strong. The radiative lifetimes of many excited states are also estimated. The A3Π0 + state at the vibrational level v‘ = 0 has the calculated radiative lifetime of 1050 ns which is somewhat larger than the observed range.

Spectroscopic investigations of the low-lying electronic states of InP have been carried out by using multireference singles and doubles configuration interaction (MRDCI) method which includes relativistic effective core potentials (RECP) of the constituent atoms. There are at least 18 Λ-S states which are bound within 44 000 cm -1 of energy. Potential energy curves of 38 Λ-S states most of which correlate with lowest three dissociation limits have been computed. The dominant configuration of the ground state (X 3 Σ -) of the molecule is σ 1 2 σ 2 2 σ 3 2 π 2 with r e ) 2.71 Å and ω e ) 248 cm -1 . The ground-state dissociation energy (D e ) of InP in the absence of the spin-orbit coupling is estimated to be 1.48 eV. However, after the inclusion of the spin-orbit interaction the D e value is reduced to 1.33 eV. All 22 Λ-S states which converge with In( 2 P)+P( 4 S) and In( 2 P)+P( 2 D) asymptotes are allowed to interact in the spin-orbit CI calculations. Effects of the spin-orbit coupling on the spectroscopic constants of lowest eight Λ-S states are studied. The zerofield splitting of the X 3 Σstate of InP has been estimated from the spin-orbit CI results. Several avoided crossings in the potential energy curves of Ω states are reported. Transition probabilities of many electric dipole-allowed transitions have been computed. Transitions such as A

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Several low-lying electronic states of GeSe up to the energy of 36 000 cm-1 have been studied by using the ab initio-based multireference singles and doubles configuration interaction calculations which include relativistic effective core potentials. Potential energy curves of 18 Λ−S states which dissociate into the ground-state limit Ge(3Pg)+Se(3Pg) have been computed. Effects of spin−orbit coupling on these states are also studied. We have also computed potential energy curves of bound Ω-states arising from those 18 Λ−S states within the energy limit of 31 000 cm-1. Spectroscopic constants (r e, T e, ωe, and βe) at equilibrium of all bound states are estimated. The ground state of GeSe is X0+ (1Σ+) originating mainly from σ2σ2σ2π4 and σ2σ2σ2π3π configurations with r e = 2.172 Å, ωe = 382 cm-1, and βe = 0.093 cm-1. The agreements with the available experimental values are fairly good. The spin−orbit interactions have little effects on the composition of the low-lying states. The transition energy of the observed A1(1Π) ← X0+ (1Σ+) transition agrees well with the calculated value. The lifetimes of the excited AΠ and 21Σ+ states are estimated to be 0.42 and 0.45 μs, respectively.