Justin Mitchell

High-resolution spectroscopy and analysis of the ν3/2ν4 dyad of CF4

CF4 is a strong greenhouse gas of both anthropogenic and natural origin [D.R. Worton et al., Environ. Sci. Technol. 41, 2184 (2007)]. However, high-resolution infrared spectroscopy of this molecule has received only a limited interest up to now. Until very recently, the public databases only contained cross-sections for this species, but no detailed line list. We reinvestigate here the strongly absorbing ν3 region around 7.8 μm. New Fourier transform infrared (FTIR) spectra up to a maximal resolution of 0.0025 cm−1 have been recorded: (i) room-temperature spectra in a static cell and (ii) a supersonic expansion jet spectrum at a 23 K estimated temperature. Following the work of Gabard et al. [Mol. Phys. 85, 735 (1995)], we perform a simultaneous analysis of both the ν3 and 2ν4 bands since a strong Coriolis interaction occurs between them, perturbing the ν3 R-branch rotational clusters around J = 20. Similarly to Gabard et al. , we also include ν4 FTIR data and microwave data in the fit. The analysis is performed thanks to the XTDS and SPVIEW programs [Ch. Wenger et al., J. Mol. Spectrosc., 251 102 (2008)]. Compared to Gabard et al. , the present work extends the analysis up to higher J values (56 instead of 32). Absorption intensities are estimated thanks to the dipole moment derivative from D. Papoušek et al. [J. Phys. Chem. 99, 15387 (1995)] and compare well with the experiment. We have produced a synthetic linelist that is included in the HITRAN 2008 and GEISA 2009 public databases. The rotational energy surfaces for the dyad are also examined in detail in order to understand the distribution and clustering patterns of rovibrational levels.

High-resolution spectroscopy and analysis of the nu3/2nu4 dyad of CF4

CF4 is a strong greenhouse gas of both anthropogenic and natural origin [D.R. Worton et al., Environ. Sci. Technol. 41, 2184 (2007)]. However, high-resolution infrared spectroscopy of this molecule has received only a limited interest up to now. Until very recently, the public databases only contained cross-sections for this species, but no detailed line list. We reinvestigate here the strongly absorbing ν3 region around 7.8 μm. New Fourier transform infrared (FTIR) spectra up to a maximal resolution of 0.0025 cm−1 have been recorded: (i) room-temperature spectra in a static cell and (ii) a supersonic expansion jet spectrum at a 23 K estimated temperature. Following the work of Gabard et al. [Mol. Phys. 85, 735 (1995)], we perform a simultaneous analysis of both the ν3 and 2ν4 bands since a strong Coriolis interaction occurs between them, perturbing the ν3 R-branch rotational clusters around J = 20. Similarly to Gabard et al. , we also include ν4 FTIR data and microwave data in the fit. The analysis is performed thanks to the XTDS and SPVIEW programs [Ch. Wenger et al., J. Mol. Spectrosc., 251 102 (2008)]. Compared to Gabard et al. , the present work extends the analysis up to higher J values (56 instead of 32). Absorption intensities are estimated thanks to the dipole moment derivative from D. Papoušek et al. [J. Phys. Chem. 99, 15387 (1995)] and compare well with the experiment. We have produced a synthetic linelist that is included in the HITRAN 2008 and GEISA 2009 public databases. The rotational energy surfaces for the dyad are also examined in detail in order to understand the distribution and clustering patterns of rovibrational levels.

Molecular Eigensolution Symmetry Analysis and Fine Structure

Spectra of high-symmetry molecules contain fine and superfine level cluster structure related to J-tunneling between hills and valleys on rovibronic energy surfaces (RES). Such graphic visualizations help disentangle multi-level dynamics, selection rules, and state mixing effects including widespread violation of nuclear spin symmetry species. A review of RES analysis compares it to that of potential energy surfaces (PES) used in Born–Oppenheimer approximations. Both take advantage of adiabatic coupling in order to visualize Hamiltonian eigensolutions. RES of symmetric and D2 asymmetric top rank-2-tensor Hamiltonians are compared with Oh spherical top rank-4-tensor fine-structure clusters of 6-fold and 8-fold tunneling multiplets. Then extreme 12-fold and 24-fold multiplets are analyzed by RES plots of higher rank tensor Hamiltonians. Such extreme clustering is rare in fundamental bands but prevalent in hot bands, and analysis of its superfine structure requires more efficient labeling and a more powerful group theory. This is introduced using elementary examples involving two groups of order-6 (C6 and D3~C3v), then applied to families of Oh clusters in SF6 spectra and to extreme clusters.