Electric dipole operator
= Electric dipole operator
{title2=$\mathbf d=\sum_a q_a\mathbf r_a$}
The <electric dipole operator> is the charge-weighted position operator of a system. It is odd under <parity> and transforms as a rank-one <spherical tensor operator>. In the nonrelativistic electric-dipole approximation it acts on spatial coordinates without directly changing spin, explaining the parity, angular-momentum and approximate spin selection rules.