The Studies Of Vibiational Spectrum Of Molecule CH₂, H₂S And HCN

With the development of modern optical instrument and improvement of experimental methods, it is become more and more fine and precision for the ro-vibrational spectrum of small molecule. But there are lots of difficults for the identification of that spectrum, the study of some spectrum band or spectrum are not success in experiment owing to all kinds of reasons. During the past fews decades, most of theoretic chemist interested in the ro-vibrational spectrum in detail for triatomic molecule. Most of variational methods have been proposed. The discrete variable representation(DVR) method is an advance technique for solving the Schrodinger equation.The methylene biradical CH₂ is of interest to both chemists and astrophysicts. In the interstellar medium, CH₂ plays an important role in the carbon chemistry, but relatively little expermental information has been available on its ground electronic states. H₂S is a kind of atmosphere contamination and is also a typical example for studying the ro-vibrational high excited spectrum of molecule. HCN is very important in astrophysicist.In this paper, we have calculated the lots of potential energy values near the equilibrium structure using the high precision method CCSD(T) and a big basis sets cc-pVTZ as implemented in the Gaussian98 package. The potential energy are fitted to several kinds of analytical functions, including Murrel-Sobie function, series expansion. Then the vibrational spectrum of those molecules in the low vibrational excited states have been studied based on above potential energy function, To solve the ro-vibrational equation, we use the DVR method. Results from our calculation are in agreement with the available experimental values and other theoretical results.