Hyperfine structure of low-lying vibrational levels in the B electronic state of molecular iodine

The hyperfine structures of the weak lines R(69) in the 3–4 band and P(84) in the 5–5 band of the B ← X electronic transition in molecular 127I2 at λ = 657 nm have been detected by the method of FM saturation spectroscopy. Frequency separations between the hyperfine components were measured, and the hyperfine coupling constants for the electric quadrupole interaction and the magnetic spin-rotation interaction were determined. For low vibrational levels of the B state, eQqB depends linearly on the vibrational energy of the level υB according to eQqB (MHz) = −0.01721G(υB) (cm−1) −484.89. ΔC is almost constant for υB values smaller than 6.