The satellite band patterns in the near ultraviolet absorption spectra of isotopic compounds of acetaldehyde

The 3700 A - 3000 A absorption spectra of CH3CHO and its isotopic compounds such as CH3CDO, CD3CHO and CD3CDO were studied in the gas phase at room temperature and low temperatures. The low resolution spectra of the compounds were recorded by a 1.5 m Baush and Lomb grating spectrograph. The high resolution spectra were recorded by a Ebert spectrograph with the Echelle grating and the holographic grating separately. The multiple reflection cells were used to achieve the long path length. The pressure-path length used for the absorption spectrum of CH 3CHO was up to 100 mm Hg )( 91 . 43mo The emission spectrum and the excitation spectrum of CH3CHO were also recorded in this research. The calculated satellite band patterns \vhich were ob-tailied by the method of Lewis were used to compare with the observed near UV absorption spectrum of acetaldehyde. These calculated satellite band patterns belonged to two cases: namely, the barriers-in-phase case and the barriers- out-of-phase case. Each of the calculated patterns corresponded to a stable conformation of acetaldehyde in the excited state . The comparisons showed that the patterns in the observed absorption spectra corresponded to the H-H eclipsed conformations of acetaldehyde in the excited state . The least squares fitting analysis showed that the barrier heights in the excited state were higher than in the ground state. Finally, the isotopic shifts for the isotopic compounds of acetaldehyde were compared to the compounds with the similar deuterium substitution.

Ribbed moraines and subglacial geomorphological signatures of interior-sector palaeo-ice sheet dynamics

Transverse, subglacial bedforms (ribbed moraines) occur frequently in southern Keewatin, Nunavut, Canada, where they record a complex glacial history, including shifting centers of ice dispersal and fluctuating basal thermal regimes. Comprehensive mapping and quantitative morphometric analysis of the subglacial bedform archive in this sector reveals that ribbed moraines are spatially clustered by size and assume a broad range of visually distinct forms. Results suggest that end-member morphologies are consistent with a dichotomous polygenetic origin, and that a continuum of forms emerged through subsequent reshaping processes of variable intensity and duration. Translocation of mobile, immobile and quasi-mobile beds throughout the last glacial cycle conditioned the development of a subglacial deforming bed mosaic, and is likely responsible for the patchy zonation of palimpsest and inherited landscape signatures within this former core region of the Laurentide Ice Sheet. Comparison against field evidence collected from central Norway suggests that bedforming processes can be locally mediated by pre-existing topography.