THE SPECTRUM OF SiH AND SiD

Abstract

Two new systems of SiH and SiD in the regions around 3 250 Å and 2 050 Å in addition to the well-known 2Δ−2Π system have been recorded in absorption and their rotational analysis (except for the 2Δ−2Π system of SiH) has been carried out. The new states are 2Σ+ at T0 = 30 974.69 cm−1 and 2Δ at T0 = 48 603.46 cm−1. The rotational constants for all the states known in SiD have been determined. The upper limit of the dissociation energy of SiH has been fixed at 24 680 cm−1 by predissociation.

An accurate description of the ground and excited states of SiH

“…Work on these two states includes the determination of ⌳-doubling transition frequencies for X 2 ⌸, 38,63,65,76 radiative lifetimes and oscillator strengths of the A 2 ⌬ϪX 2 ⌸ system, 43,45,47,61,64,74 various molecular constants, 55,56,67,72,78,79,84 transition moments, 66 ionization potentials, 55,80,81 and dissociation energies and enthalpies of formation. 55,59,64,68,80,81,83 To our knowledge, only a limited number of experimental papers deal with the higher excited states, but the extracted parameters useful to the present theoretical work are very few, limited mostly to term values. These papers include the work of Verma, 55 Herzberg et al, 60 Bollmark et al, 62 and Johnson and Hudgens.…”

“…55,59,64,68,80,81,83 To our knowledge, only a limited number of experimental papers deal with the higher excited states, but the extracted parameters useful to the present theoretical work are very few, limited mostly to term values. These papers include the work of Verma, 55 Herzberg et al, 60 Bollmark et al, 62 and Johnson and Hudgens. 82 The latter authors have located a state at 46 700Ϯ10 cm Ϫ1 and identified it as either a 2 ⌸ or a 2 ⌺ ϩ state.…”

Ab initioMRD-CI study of the electronic spectrum of SiH

“…The second system, B 2E+-X 2IIr at 3250 A first observed by Verma [5], exhibits a very complicated and irregular pattern and seems to be strongly predissociated above N=2 in Sill. Various extra lines could not be fitted into the B state model [5].…”

“…The second system, B 2E+-X 2IIr at 3250 A first observed by Verma [5], exhibits a very complicated and irregular pattern and seems to be strongly predissociated above N=2 in Sill. Various extra lines could not be fitted into the B state model [5]. Herzberg et al [7] 2 M. Lewerenz et al suggest a 2E+ or 21-I perturbing state with a minimum at large internuclear separation as the cause for the predissociation, whereas Bollmark et al [10], who report a rotational analysis of the B 2Y.+-X 21J r band, assume that there might be several perturbing states responsible for the irregular character in the spectrum.…”

“…Of all electronic transitions which have been observed for Sill and SiD only the lowest, A ~A-X ~H r at 4128 A, that is the analogue to the 4315 A band in CH, has been fully analysed [5][6][7][8][9]. The second system, B 2E+-X 2IIr at 3250 A first observed by Verma [5], exhibits a very complicated and irregular pattern and seems to be strongly predissociated above N=2 in Sill.…”