Overlapping (BII0u)-I-3 <- X-1 Sigma(+)(g) and (II1u)-I-1 <- X-1 Sigma(+)(g) non-radiative characteristic of Br-2 vapour in the wavelength region 505-541 nm

The vibronic vapour phase photoacoustic spectrum of Br-2 in the wavelength region 505-541 nm (19796-18480 cm(-1)) has been recorded using microphone a s well as pump-probe method. Discrete vibronic bands superimposed on a mono tonically increasing continuum background towards the dissociation limit re sults from the overlapping (BII0u+)-I-3 <-- X-1<Sigma>(+)(g) and (II1u)-I-1 <-- X-1<Sigma>(+)(g) electronic transitions. Vibronic bands originating fr om nu " = 0 have been used to estimate the relative rate of non-radiative r elaxation as a function of the excited state B (II0u)-I-3, vibrational quan tum number nu '. A comparison with the optical absorption spectroscopy of B r-2 leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm(-1)) on the basis of different non-radiativ e relaxation processes.