A new inversion coordinate is defined for ammonia as a function of the valence angles. Its square is similar to the often used totally symmetric bending displacement coordinate for the pyramidal XY3–type molecules. We have used this in a two-dimensional calculation including the totally symmetric stretching and the inversion mode. A conventional symmetrized internal coordinate is employed for the symmetric stretch. A two-dimensional potential energy surface is calculated using the ab initio CCSD(T) method together with the aug-cc-pVTZ, cc-pVQZ, and aug-cc-pVQZ basis sets. The corresponding eigenvalues are calculated variationally using a Morse oscillator basis set for the stretch and a harmonic oscillator basis set for the inversion. A good agreement is obtained between the calculated and 22 experimental inversion levels, 9 of NH314 and the others involving 4 other isotopomers (14ND3, NH315, ND315, and NT314). With the aug-cc-pVTZ basis, a mean absolute error of 5.0 cm−1 is obtained whereas with the aug-cc-pVQZ basis set the error becomes 7.9 cm−1.

Kulmala (2020): Determination of the collision rate coefficient between charged iodic acid clusters and iodic acid using the appearance time method, Aerosol Science and Technology,

No abstract

The gradients of vibrational coordinates are needed in order to form the exact vibrational kinetic energy operator of a polyatomic molecule. The conventional methods used to obtain these gradients are often quite laborious. However, by the methods of geometric algebra, the gradients for any vibrational coordinate can be easily calculated. Examples are given, and special attention is directed to ring coordinates.

No abstract