Hyperfine structure near the 13–1 band head in the B–X transition of ^127I_2

Hyperfine structure of the rovibronic transitions R(0)–R(10) and P(1)–P(5) in the 13–1 band belonging to the B–X system of 127I2 was studied by rectangular-crossing molecular-beam laser spectroscopy. The full width at half-maximum of the observed lines was 5 MHz, which corresponds to a resolving power of 108. Not only allowed transitions ΔF = ΔJ but forbidden transitions ΔF = 0 and ΔF = −ΔJ were identified, and absolute hyperfine coupling constants of the rovibronic states (J = 0–10) in the B(v′ = 13)−X(v″ = 1) transition were determined. In addition, the relative line strength of each hyperfine transition was compared with the theoretical value.