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3700{\AA} MAGNETIC ROTATION SPECTRUM OF PYRAZINE (1,4-DIAZINE).

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/14807

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Title: 3700{\AA} MAGNETIC ROTATION SPECTRUM OF PYRAZINE (1,4-DIAZINE).
Creators: Snowden, B. S., Jr.; Eberhardt, William H.
Issue Date: 1965
Abstract: The absorption spectrum of pyrazine above 3000{\AA} consists of strong bands around 3100{\AA} corresponding to a singlet-singlet transition and a group of less intense bands around 3700{\AA} corresponding to a triplet-singlet $transition.^{1}$ Using magnetic rotation techniques, only those bands corresponding to the 3700{\AA} triplet-singlet transition were observed. This was expected, because according to our present understanding of the theory of magnetic rotation $spectra,^{2}$ only those bands corresponding to a triplet-singlet transition would be expected to exhibit a magnetic rotation spectrum. The appearance of the band envelopes of the pyrazine bands at 3727{\AA} and 3642{\AA} was greatly affected by rotation of the analyzing prism. In the usual magnetic rotation experiment with the prisms crossed the 3727{\AA} band appears as a sharp feature. When the analyzing prism is rotated in a clockwise direction by one half a degree, the observed magnetic rotation spectra appears to be blackened on the high energy side of the sharp feature. However, when the analyzing prism is rotated one half of a degree counter clockwise, there is a blackening of the magnetic rotation spectrum on the low energy side of the sharp features. According to $Innes,^{3}$ the 3727{\AA} band of pyrazine observed in absorption corresponds to a triplet-singlet transition. The rotational fine structure in this band above $26,820 cm^{-1}$ is thought to be built up of branches corresponding to the selection rules $\Delta K = +2$ and $\Delta N = + 1$ and that below $26,820 cm^{-1}$ to be caused by a pile up of branches corresponding to the selection rules $\Delta K = -2$ and $\Delta N = -1$. The central sharp feature found in the magnetic rotation when the prisms are crossed occurs at $26,820 cm^{-1}$, the band origin of the absorption spectrum.
URI: http://hdl.handle.net/1811/14807
Other Identifiers: 1965-I-5
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