Abstract
The rates of tunnelling through the barrier in the A 1Π state of BH are inferred from the total lifetimes measured by Gustaffson and Rittby. A theoretical analysis of the tunnelling process allows the determination of the height and width of the barrier and, indirectly, the dissociation energy of BH in the ground state: D e = 29 420 ± 30 cm-1. This value is higher than that previously accepted (28 760 ± 150 cm-1), but it agrees with the most accurate ab-initio results.