Rotation dependence of electric quadrupole hyperfine interaction in the ground state of molecular iodine by high-resolution laser spectroscopy

Doppler-free high-resolution spectroscopy is applied to molecular iodine at 532 nm by Nd:YAG lasers. The main hyperfine components as well as the crossover lines are measured for R(56)32-0 and P(54)32-0 transitions by heterodyne beating of two I2-stabilized lasers. The measured hyperfine splittings including both main and crossover lines are fitted to a four-term Hamiltonian, which includes the electric quadrupole, spin–rotation, tensor spin–spin, and scalar spin–spin interactions, with an average deviation of ∼1 kHz. Absolute values of the electric quadrupole hyperfine constants for both the upper and the lower states are obtained. The rotation dependence of the ground-state (v″=0) electric quadrupole constant eQq″ is found to be eQq″(J)=-2452.556(2)-0.000164(5)J(J+1)-0.000000005(2)J2(J+1)2 MHz.