Knowledge Bank

A free electron theory for naphthalene based on an electron moving in the path $\rho =\rho 0(1+2\ell \cos \varphi )12$ is developed. This theory predicts (for $\ell =12$, two contiguous circles) an oscillator strength of one along the long axis and zero along the short axis. This is in qualitative agreement with the predictions of valence-bond theory and molecular-or-bital theory with configuration interaction. An experimental study of the absorption of polarized light by thin naphthalene crystals has been carried out; and it has been established that the crystal absorbs more strongly light directed normal to the crystal face which is polarized parallel to the b-axis than that which is polarized perpendicular to this axis. If it may be assumed that the absorption of the long-wavelength band in a given direction parallels the refractive index, then the absorption result checks the experimentally determined indicatrix. Then from the orientation of the indicatrix in the unit cell, and subject to the above assumption, it is concluded that the longest-wavelength band in naphthalene is polarized along the long axis of the molecule.