On the Predissociation of Several Diatomic Molecules

Abstract

From the observed anomalous intensity distribution in the S2 bands it is concluded that the dissociation limit for the first predissociation of S2 lies appreciably below the predissociation limit (4.4 ev). It is found that the anomalous intensity as well as the diffuseness persists even at very low pressures (0.01 mm) and that therefore this is a case of genuine predissociation and not pressure broadening as assumed by Lochte-Holtgreven. The second predissociation of S2 starting with the 18 - 0 band leads to an upper limit of 3.6 ev for the heat of dissociation of S2. An anomalous intensity distribution similar to that of S2 is found for NO assuming that the ε absorption bands are a continuation of the γ bands. This indicates a predissociation of NO in the upper 2Σ state of the γ bands into normal atoms with a limit 1.3 ev above the dissociation limit. The remarkable intensity distribution found by Schüler and co-workers in the CuH emission band λ4280 at low pressure is explained as due to a predissociation into the 3Σ+ state derived from normal Cu(2S) and normal H(2S). Such a state cannot cause the predissociation of the level J′ = 0 in agreement with observations. The heat of dissociation of CuH comes out to be <23,325 cm-1 (i.e., <2.892 ev). The method previously suggested by one of the authors for the detection of maxima of potential curves is applied to AlD (AlH) and BH. From the breaking off points observed in the visible bands of these molecules it is established that their 1II states have potential curves with maxima. Therefore the dissociation energies are appreciably lower than the energies of the observed breaking off points, i.e., D0(AlH) <24,775 cm-1, D0(AlD) <25,010 cm-1, D0(BH) <28,350 cm-1.