15min:

XINCHUAN HUANG, MS 245-6, NASA Ames Research Center, Moffett Field, CA, 94035; DAVID W. SCHWENKE, MS T27B-1, NASA Ames Research Center, Moffett Field, CA, 94035; TIMOTHY J. LEE, MS 245-1, NASA Ames Research Center, Moffett Field, CA, 94035.

A further refined, global potential energy surface (PES) is computed for the C_3v symmetry isotopologues of ammonia, including ¹⁴NH₃, ¹⁵NH₃, ¹⁴ND₃ and ¹⁴NT₃. The refinement procedure was similar to that used in our previously reported PES, but now extends to higher J energy levels and other isotopologues. Both the diagonal Born-Oppenheimer correction and the non-adiabatic correction were included. J=0-6 rovibrational energy levels and transition frequencies of ¹⁴NH₃ computed on this PES are in excellent agreement with HITRAN data. Statistics on nearly 4100 transitions and more than 1000 energy levels demonstrate the accuracy achieved by the state-of-the-art "Best Theory + Experiment" strategy. Most transition frequencies are of \pm0.01-0.02 cm^-1 accuracy. Similar accuracy has been found on ¹⁵NH₃ J=0-3 rovibrational energy levels. Several transitions and energy levels in HITRAN have been identified as unreliable or suspicious, and some have been re-assigned. For ¹⁴ND₃ and ¹⁴NT₃, J=0-3 calculations have been performed. Agreement for pure rotation-inversion transitions is nearly perfect, with more reliable energy levels presented. On the other hand, our J=0 results suggest a re-analysis on the ¹⁴ND_{3 1} band origin is needed. Finally, we will discuss possible future refinements leading to an even better final PES for Ammonia.