NEW ANALYSIS OF THE PENTAD SYSTEM OF METHANE AND PREDICTION OF THE (PENTAD-PENTAD) SPECTRUM

The pentad system (nu(1), nu(3), 2 nu(2), nu(2) + nu(4), 2 nu(4)) of m ethane (CH4)-C-12 has been reanalyzed with a partly reduced fourth-ord er (206 parameters) Hamiltonian for energy levels and a second-order ( 13 parameters) dipole moment expansion for infrared intensities. In ad dition to infrared data. new experimental observations have been used: infrared hot bands (pentad-dyad), Raman bands, and microwave transiti ons among nu(3) levels. The obtained standard deviations (for J less t han or equal to 18) have the same order of magnitude as the experiment al accuracies (0.001-0.002 cm(-1) for infrared or Raman wavenumbers, 8 0 kHz for microwave frequencies, and 8% for infrared intensities). In view of atmospheric or planetary applications, improved predictions of the infrared methane spectrum, including weak absorptions, are availa ble. A prediction of the (pentad-pentad) spectrum is also given to sug gest further possible microwave observations. (C) 1994 Academic Press, Inc.