Knowledge Bank

Method was derived which give possibility to obtain intramolecular potential function of methane molecule directly from experimental data on high-resolution vibration-rotation spectra. As the initial information experimental data on $\mathrm{<mrow\; data-mjx-texclass="ORD">\sim </mrow>}40$ vibration-rotation bands of $CH2D2$ molecule and on $\mathrm{<mrow\; data-mjx-texclass="ORD">\sim </mrow>}15$ bands of $CH4$ molecule were used. Presence of very strong Fermi resonance interactions between some bands of $CH2D2$ molecule $(e.g.,\nu 4+\nu 8and2\nu 4+\nu 9,\nu 3+\nu 8and\nu 3+\nu 4+\nu 9,etc.)$ gave possibility to determine correctly some force $fi..j$ constants, which have not been obtained correctly in earlier semiempirical $analysis1,2$. To put to the test correctnicy of determined intramolecular force field, parameters of spectral lines of other methane isotopic species $(CH3D,CHD3,CD4,etc.)$ were calculated and compared with corresponding experimental data. Work was supported by the grant of Russian Foundation of Fundamental Researches N94-02-03081-a.