Abstract:
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.
