Revisiting the photoabsorption spectrum of NH₃ in the 5.4-10.8 eV energy region

We present a comprehensive revisited experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of ammonia, NH₃, covering for the first time the full 5.4-10.8 eV energy-range, with absolute cross sections determined. The calculations on the vertical excitation energies and oscillator strengths were performed using the equation-of-motion coupled cluster method restricted to single and double excitation levels and used to help reanalyze the observed Rydberg structures in the photoabsorption spectrum. The VUV spectrum reveals several new features that are not previously reported in the literature, with particular reference to the vibrational progressions of the (D'1EX'1A1′), the (F'1EX'1A1′), and the (G'1A2X'1A1′) absorption bands. In addition, new Rydberg members have been identified in nda11a2″D'′′1A2X'1A1′, where n > 3 has not been reported before as well as in nde1a2″F'1EX'1A1′ and in nsa1 1a2″G'1A2X'1A1′. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of ammonia in the Earth's atmosphere (0-50 km).