A Comment on Zeeman Effects in Rotation Spectra
Abstract Recently SUTTER et al. 1 obtained a Hamiltonian for a molecule in the presence of a constant external elec-tromagnetic field. (A similar Hamiltonian has been de-veloped 2 , but including molecular vibrations, relativis-tic corrections and allowance for the fact that the mo-lecular centre of gravity differs from the nuclear centre of gravity.) We believe that the Hamiltonian of Sutter et al. is not correct, since they make two errors of principle in performing their gauge transformation. They start with a Lagrangian expressed in terms of the particle positions, rn\ in a space-fixed coordinate system. Each particle is associated with an external vector potential,-^«' = rn', where H is the constant external magnetic field. At this stage a gauge transfor-mation may be performed: An'-+An'-VnX, (1)