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

Publisher Website
Google Scholar
Abstract
The dipole strengths for certain perpendicular-type transitions N→Q in 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 the N→Q transitions in F2, Cl2, and Br2. The iodides, however, just like I2, show anomalously low strengths for the true N→Q part of the intensity (N→3II1 and N→1II), together with high strength for N→3II0+. These anomalies are ascribed here, as in I2, to partial case c coupling (partial preservation of atomic J's). The comparison between theory and experiment confirms the interpretation of the ultraviolet continua of the hydrogen and alkyl halides as N→Q transitions. Dipole strength calculations for the well-known 2Σ→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 the N→Q dipole 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, 5p orbitals) than for those containing fluorine (2p orbital). They are also larger for hydrogen halides than for corresponding halogens.