Knowledge Bank

%took out renew command Methane is an important prototype for intramolecular dynamics [1] and of relevance in a variety of spectroscopic contexts [2]. We measured the infrared spectrum of CH$2$D$2$ at 78 K in the range 2800 - 6600 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ with the Z$u¨$rich high resolution (up to 0.0007 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) Fourier transform interferometer Bruker IFS 125 prototype (ZP 2001) equipped with an enclosive flow cooling cell. More than 75 vibrational bands were newly assigned and analyzed rovibrationally. Precise ($\sim$ 0.0001 - 0.0003 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) experimental band centers were combined with previously known band centers (93 altogether) and used as the initial information for the determination of the set of 9 "harmonic" ($\omega ~\lambda$) and 41 quartic anharmonic ($x\lambda \mu$) parameters, as well as 7 resonance interaction parameters. The derived set of effective Hamiltonian parameters reproduce the vibrational structure of the CH$2$D$2$ molecule up to 6600 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ with a $rms$ deviation of 0.54 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$.\ The data obtained were used then for estimating of "experimental" values of $Fij$, $Fijk$, and $Fijkl$ force constants of the methane intramolecular potential function. The comparison of these with the earlier experimental and \textit{ab initio} results is discussed.\ [1] R. Marquardt and M. Quack, J. Phys. Chem. A 108, 3166 (2004) (and references cited therein). [2] O. N. Ulenikov, E. S. Bekhtereva, S. V. Grebneva, H. Hollenstein, and M. Quack, Phys. Chem. Chem. Phys. 7, 1142 (2005) (and references cited therein).\