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, NH, 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).
M.M. and F.F.S. acknowledge the Portuguese National Funding Agency FCT-MCTES through Grant No. PD/BD/106038/2015 and researcher position IF-FCT IF/00380/2014, respectively, and together with A.I.L. and P.L.-V. the research Grant Nos. UID/FIS/00068/2019 (CEFITEC), PTDC/FIS-AQM/31281/2017, and PTDC/FIS-AQM/31215/2017. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, Grant No. PD/00193/2012) and Grant No. UID/Multi/04378/2013 (UCIBIO). P.L.-V. also acknowledges his visiting professor position at Sophia University, Tokyo, Japan. The authors wish to acknowledge the beam time at the ISA synchrotron radiation source ASTRID2, Aarhus University, Denmark. D.D. acknowledges the support of the grants OVERSEE and CAPPA, managed by the Agence Nationale de la Recherche, Contract Numbers ANR-16-IDEX-0004 ULNE (I-SITE ULNE) and ANR-10-LABX-005 (CAPPA). D.D. also thanks the Région Hauts de France, the Ministère de l’Enseignement Supérieur et de la Recherche (CPER Climibio), and the European Fund for Regional Economic Development for their support. This work used HPC resources from GENCI-TGCC (Grant No. 2019-A0010806820) and the Centre de Ressources Informatiques (CRI) of the Université de Lille. G.G. acknowledges partial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (Project No. FIS2016-80440) and CSIC (Project No. LINKA20085). This work was conducted under the support of the Ministry of Education, Culture, Sport, Science and Technology (MEXT), Japan.