The 0.9 eV Absorption Band of Polyaniline: A Morphologically Sensitive Electronic Absorption

The optical absorption spectra of polyaniline in the visible and UV spectral regions have been characterized before. The electrically conductive form has a band gap absorption at 3.8 eV and polaron absorptions at 2.9 and 1.5 eV [1,2] . An additional electronic absorption band at 0.9 eV was found to be also related to the existence of polaron. The assignment of this transition has yet to be made. Epstein and co-workers [31 have found a photo-induced absorption band at 0.9 eV by photo-exciting emeraldine base (insulator) with 2.0 eV light. It is not known yet whether these two 0.9 eV transitions belong to the same set of electronic energy levels of polaron, or they belong to two different electronic systems but are coincidentally have the same transition energy.

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The ultra-violet spectrum of magnesium hydride. 1.—The band at λ 2430

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1929.0033 ◽

1929 ◽

Vol 122 (790) ◽

pp. 442-455 ◽

Cited By ~ 22

Keyword(s):

Fine Structure ◽

General Structure ◽

Energy Levels ◽

Visible Region ◽

Ultra Violet ◽

Present Theory ◽

Magnesium Hydride ◽

Electronic Energy ◽

Band Spectra ◽

Electronic Energy Levels

The system of bands in the visible region of the emission spectrum of magnesium hydride is now well known. The bands with heads at λλ 5622, 5211, 4845 were first measured by Prof. A. Fowler, who arranged many of the strongest lines in empirical series for identification with absorption lines in the spectra of sun-spots. Later, Heurlinger rearranged these series in the now familiar form of P, Q and R branches, and considered them, with the OH group, as typical of doublet systems in his classification of the fine structure of bands. More recently, W. W. Watson and P. Rudnick have remeasured these bands, using the second order of a 21-foot concave grating, and have carried out a further investigation of the fine structure in the light of the present theory of band spectra. Their detection of an isotope effect of the right order of magnitude, considered with the general structure of the system, and the experimental work on the production of the spectrum, seems conclusive in assigning these bands to the diatomic molecule MgH. The ultra-violet spectrum of magnesium hydride is not so well known. The band at λ 2430 and the series of double lines in the region λ 2940 to λ 3100, which were recorded by Prof. Fowler in 1909 as accompanying the group of bands in the visible region, appear to have undergone no further investigation. In view of the important part played by hydride band spectra in the correlation of molecular and atomic electronic energy levels, it was thought that a study of these features might prove of interest in yielding further information on the energy states of the MgH molecule. The present paper deals with observations on the band at λ 2430; details of an investigation of the other features of the ultra-violet spectrum will be given in a later communication.

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