THEORETICAL INVESTIGATION OF THE LOW-LYING ELECTRONIC STATES OF TIH

The vertical excitation energies of thirty electronic states of TiH as well as the potential curves of all quartet and doublet states correlating with the first two channels Ti + H have been investigated by using extensive MRD-CI calculations. Based on the results for the transition energies and dipole transition moments, the known absorption bands extending from 18 200 to 21300 cm-1 (a strongest band near 18870cm-1 assumed to be a X4Φ→4Δ transition) are assigned to transitions from X4Γ into 1=4 ⌈ (calculated Twert= 17420cm-1) and into 44Δ (calculated Tvert= 19440cm-1), with possible contribution of the excitation 14Σ-→54Π (calculated Tvert = 17500 cm-1). These strong (perpendicular) 8σ→4π bands lie rather close to the measured excitation energies assigned to the dipole allowed high-intensity transition 4s →4p of the Ti atom. In addition the present study shows that two TiH bands of relatively high-intensity lie near 11000cm-1 (i.e. X4Φ→ 24Φand 14Σ-→24Σ), a prediction awaiting its experimental verification. The low-energy (parallel) 8σ→6σ (3d) bands have Te values about 4500 cm-1 higher than the equivalent 4s → 3d atomic transition. The term values for the first TiH Rydberg members4Φ and4Π (both 8σ→5s states lying slightly above 32000 cm-1) compare well with the experimental 4s →5s term values of the Ti atom. The analysis of the bonding in the 12Δ and 12Π states shows that these states have contributions from 3dσ (Ti), and as a consequence have shorter equilibrium distances than their quartet counterparts. States with sextet multiplicity are repulsive. The calculated dipole moment μ at R (TiH) = 3.47 a.u. for all bound states from channels I and II reveal a strong dependency of n on the relative occupation of 6a(3da) and 8<7, as pointed out by a low µ of 0.92 D for 14Δ (lδ6σ7σ28σ) and a high n of 4.61D for 24Δ (1δ3π7σ8). Between both extreme values, other examples are provided by μ= 1.90 for X4<D (WinlaHa) and µ = 2.83D for 24Φ(1 π3Π7σ2 8σ). © 1990 Taylor & Francis Ltd.