Diode laser spectroscopy of ammonia at 760 nm

A tunable diode laser spectrometer has been employed to examine the unknown overtone absorption lines of NH3 around 13100 cm-1 (760 nm). The spectrometer sources are commercially available heterostructure AlGaAs tunable diode lasers operating in the "free-running" mode. The detection of the lines has been possible by the use of the wavelength modulation spectroscopy and the second harmonic detection technique. A special algorithm has been used in order to fit the highly modulated absorption lines. The weakest observed resonances have absorption cross sections on the order of ~ 1 x 10-25cm2/molecule or ~ 0.3 km-1/amagat. For some of the more intense lines self-, air-, N2-, He- and H2-broadening coefficients have been obtained at room temperature and also some shifting coefficients have been measured.