Chemical Physics Letters, Vol.692, 319-323, 2018
The sign of the polarizability anisotropy of polar molecules is obtained from the terahertz Kerr effect
The terahertz Kerr effect (TKE) of polar molecular vapors is reported. The birefringence signal of fluoroform appears with opposite polarity compared to acetonitrile and water. This behavior is a hallmark of the opposite sign of a new molecular polarizability anisotropy Delta alpha(TKE) = alpha(zz) - (alpha(xx) +alpha(yy))/2 with alpha(zz) being the polarizability along the permanent dipole moment. As the excitation of the rotational states orients the permanent dipoles along the terahertz electric field, the orientation is translated into an optical birefringence proportional to Delta alpha(TKE). Thus, the sign of Delta alpha(TKE) is imprinted onto the TKE signal, providing novel insights into the polarizability tensor of water. (C) 2017 Elsevier B.V. All rights reserved.