Intrinsic reaction coordinate calculations of the inversion/bending potentials in the (X)over-tilde and (A)over-tilde states of ammonia

Mass-weighted intrinsic reaction coordinate calculations were carried out f or the inversion/bending motion in the ground and lowest excited singlet st ates of NH3 and ND3. Vibrational eigenstates were obtained from these IRC p otentials directly, obviating the need to make assumptions about the coordi nate dependence of the reduced mass. The 0(+/-) inversion splittings for th e (X) over tilde state of NH3 and ND3 are found to be 1.17 and 0.89 cm(-1), respectively, at the MP4(SDQ)/aug-cc-pVTZ level of theory. CASPT2-refined IRC scans of both the relaxed and vertical (A) over tilde -state surfaces w ere carried out. The (A) over tilde-(X) over tilde absorption spectra of NH 3 and ND3 were modeled using the respective Boltnnann-weighted vibrational electronic transition matrix elements. (C) 2001 Elsevier Science B.V. All r ights reserved.