Intensities in Molecular Electronic Spectra X. Calculations on Mixedhyphen;Halogen, Hydrogen Halide, Alkyl Halide, and Hydroxyl Spectra

摘要

The dipole strengths for certain perpendicular‐type transitionsN→Qin the mixed halogens, the hydrogen and monovalent metal halides, and the alkyl halides, are calculated theoretically by the LCAO and by the AO approximations. The scanty experimental absorption coefficient data on these halides (particularly the hydrogen and alkyl bromides and iodides) are critically examined, and acceptable experimental dipole strengths are obtained for the bromides. These show, very gratifyingly, the same kind of agreement with the calculated values as was found in IX of this series for theN→Qtransitions in F2, Cl2, and Br2. The iodides, however, just like I2, show anomalously low strengths for the trueN→Qpart of the intensity (N→3II1andN→1II), together with high strength forN→3II0+. These anomalies are ascribed here, as in I2, to partial caseccoupling (partial preservation of atomicJ's). The comparison between theory and experimentconfirms the interpretation of the ultraviolet continua of the hydrogen and alkyl halides as N→Q transitions.Dipole strength calculations for the well‐known2&Sgr;→2II transition in OH have also been made. The agreement with Oldenberg and Rieke's experimental values for OH is of much the same kind as for the other molecules. A general equation for theN→Qdipole strength in AX or OH is obtained covering any degree of ionicity and of polarity. This includes the AO and LCAO approximations, with any degree of polarity, as special cases. It is found that the intensity is on the whole not especially sensitive to polarity. The magnitudes of overlapping and dipole strength integrals in relation to molecular stability and to principal quantum number of the valence orbital are discussed. The integrals are notably larger for molecules containing the heavier halogens (3p,4p,5porbitals) than for those containing fluorine (2porbital). They are also larger for hydrogen halides than for corresponding halogens.