The vibrational frequencies of ozone

The equilibrium structure and harmonic frequencies of ozone have been determined at various levels of coupled-cluster theory using large one-particle basis sets. We have used the singles and doubles coupled-cluster (CCSD) method, the recently proposed CCSD(T) method, and the CCSDT-1 method. The largest one-particle basis sets utilize the atomic natural orbital (ANO) general contraction scheme and contain up through g-type functions. It is shown that f-type functions are essential for obtaining quantitative accuracy in the equilibrium structure and the harmonic frequencies (i.e.,±0.003 Å and ± 30 cm−1). The CCSD(T) level of theory in conjunction with a 4s 3p 2d 1f ANO basis set is found to yield an equilibrium geometry and harmonic frequencies in excellent agreement with experiment. At this level of theory the harmonic frequencies are ω1(a1)=1152, ω2(a)1=717, and ω3(b2)=1057 cm−1 to be compared with the experimental values of 1135, 716, and 1089 cm−1, respectively. This success encouraged us to determine the cubic and quartic force constants and evaluate the anharmonic corrections to the fundamental vibrational frequencies. This level of theory is shown to be quite good for the a1 vibrational modes, but some of the cubic force constants involving ω3(b2) are shown to have large errors leading to an anharmonic correction for the asymmetric stretch that is about a factor of 2 too large.