Variational Calculation of Highly Excited Rovibrational
Energy Levels of H<sub>2</sub>O<sub>2</sub>
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Abstract
Results are presented for highly
accurate ab initio variational
calculation of the rotation–vibration energy levels of H<sub>2</sub>O<sub>2</sub> in its electronic ground state. These results
use a recently computed potential energy surface and the variational
nuclear–motion programs WARV4, which uses an exact kinetic
energy operator, and TROVE, which uses a numerical expansion for the
kinetic energy. The TROVE calculations are performed for levels with
high values of rotational excitation, <i>J</i> up to 35.
The purely ab initio calculations of the rovibrational energy levels
reproduce the observed levels with a standard deviation of about 1
cm<sup>–1</sup>, similar to that of the <i>J</i> =
0 calculation, because the discrepancy between theory and experiment
for rotational energies within a given vibrational state is substantially
determined by the error in the vibrational band origin. Minor adjustments
are made to the ab initio equilibrium geometry and to the height of
the torsional barrier. Using these and correcting the band origins
using the error in <i>J</i> = 0 states lowers the standard
deviation of the observed–calculated energies to only 0.002
cm<sup>–1</sup> for levels up to <i>J</i> = 10 and
0.02 cm<sup>–1</sup> for all experimentally known energy levels,
which extend up to <i>J</i> = 35