A new spectrum in the region 3115–2680 Å has been obtained in absorption by a flash discharge technique, and is attributed to the PO2 radical. Vibronic and K structure analyses are performed which show conclusively that the new spectrum is analogous to the 2490 Å system of NO2, and thus represents the [Formula: see text] transition of the PO2 radical. The vibronic assignments are confirmed by an isotopic study of the spectrum using oxygen-18. The various frequencies obtained are: [Formula: see text], [Formula: see text], and [Formula: see text]. A predissociation is observed from which an upper limit to the energy of dissociation into P + O2 is set at 35 500 ± 100 cm−1.
Intense spectra of HSiCl and HSiBr in the region 6000 to 4100 Å have been obtained in the flash photolysis of SiH3Cl and SiH3Br, both in absorption and in fluorescence. They consist of progressions of bands with very wide K structures and very narrow J structures. A detailed fine structure analysis of these bands has been carried out and the geometrical structure of the molecules in both the upper and the lower states has been established. For the lower state, probably the ground state of HSiCl, it is found that[Formula: see text]and similarly for HSiBr[Formula: see text]In the excited states the angles are appreciably larger (see Table XI).A striking feature of the band structure in both HSiCl and HSiBr is the occurrence of branches of subbands with ΔK = ± 2, in addition to those with ΔK = ± 1 and 0, and furthermore, the presence of a subband with K = 0 in the branch with ΔK = 0. These anomalies can be accounted for by the assumption that the electronic transition is a triplet–singlet transition, more specifically 3A″–1A′ (or possibly 1A′–3A″). However, no triplet splitting has been resolved in the spectrum.
Three band systems of Si2 have been found in absorption with a flash photolysis apparatus. Two of the band systems at 3200 and 2100 Å are new, whereas the third is an extension of the 3Σ–3Σ system observed by Douglas in emission. All three systems have the same lower state and arise from [Formula: see text] transitions. It is very probable that the [Formula: see text] state is the ground state of the Si0 molecule. Rotational and vibrational constants of all four 3Σ states have been determined. The dissociation energy of Si2 is estimated to be 3.0 ± 0.2 ev.
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.
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