Absor ption Spec trum of S O۲ Molecule: Including S۱–S۲ Vibroni c Coupling

In this w ork, we pr esent a mod el Hamilto nian including three vib rational mo des of sulfur dioxide molecule an d determine the potential energy surfaces of the lowest two excited states S۱[۱A۲] a nd S۲[۱B۱], which are strongly cou pled to each other [۱]. The leading c oefficients of the Taylor expansio n of the diabatic pote ntial-energ y surfaces i n terms of ground-state normal coordinates at the reference geometry have been obta ined [۲] at the CIS/ ۶- ۳۱۱++G( ۳df, ۳pd) level. The g as phase absorption s pectrum of SO۲ molecule has bee n calculated in the ۲۴۰۰–۳۴۰۰ ǖ regions using the time c orrelation theory, including vibronic coupling. The absorption spec trum is in acceptable agreement with the experimental spectrum . As is well known the symmetry of SO۲ molecule is C۲V. It has three normal modes, in which, symmetry stretching a nd bending are classifie d into a۱ and anti symme try stretchin g into b۲. T he optimize d geometri c parameters , the calcula ted electron ic transition energies an d their osc illator stre ngths for th e ۱A۲ and ۱ ۱B۱ states of SO۲ are calculated. For both electronic states, the computed bond length s and angle s seems to be highly consistent an d reliable results can be obtained with SA C-CI/DGDZVP level. The adiabatic vibrational frequencies calculated at various levels of theory for the ۲ ۱A۱ and ۱ ۱B ۱ states. T he vibrational frequencies calculat ed of the ۱ A۲ and ۱B۱ states give the best agreement with experime ntal values. For the purpose of obtaining corre ct estimates of the multidimensional time do main integrals and abs orption cro ss sections, the theor etical meth od should be selected from the vi ewpoint of whether it can provide sufficiently correct analytic gradients and second derivati ves of excited adiabatic potential e nergy surfaces (۱A۲ an d ۱B۱) at t he ground state.

کلیدواژه ها:

Vibronic coupling ، T ime correlation theory ، Absorption spectrum ، SO۲ molecul e