LONG WAVELENGTH VIBRONIC TRANSITIONS OF $^{79}BrCl$ AND $^{81}BrC1$

$^{1}$ J.A. Coxon, J. Mole, Spectry., 50, 142-165 (1974). $^{2}$ D.L. Albritton, A.L. Schmeltekopf, and R.N. Zare, An Introduction to the Least-Squares Fitting of Spectroscopic Data, in Modern Spectroscopy, Modern Research 11, K.N. Rao, ed, Academic Press, NY, 1976.Author Institution: AFWL/ARSI, Air Force Weapons LaboratoryA technique was developed by which the vibronic spectrum of bromine monochloride was observed from laser induced fluorescence at long wavelengths. An RCA C31034 PMT was used to detect short wavelength emissions (650-890nm) and an ADC cooled germanium infrared detector was used to detect long wavelengths $(809nm-1.1\mu)$. The vibrational band heads were spectrally resolved with a resolution of 0.2nm at 650-890nm and 1.0nm at $890nm-1.1\mu$. This resolution allowed the separation and characterization of the bandheads for the two bromine isotopes. The signal from the ADC detector was passed through a lock-in amplifier. A computer controlled data acquisition system allowed the signal from the lock-in to be averaged at each spectral point for 100-400 signals. This technique increased signal to noise substantially and allowed the observation of previously unreported transitions so that band heads could be readily reported. These studies allowed the extension of the spectral observations of Coxon (1) on BrCl. The newly observed transitions ranged from $v^{\prime}=3 \longrightarrow v^{\prime\prime}=5$ to $v^{\prime}=0 v^{\prime\prime}=19$. Molecular constants were calculated from the values for the band head positions by means of a merging technique (2). The calculated constants were compared with those reported by Coxon (1) for shorter wavelength transitions. The correspondence between the constants will be discussed