Vacuum-ultraviolet absorption spectrum of acetaldehyde, CH3CHO, and the related deuterides CH3CDO and CD3CDO

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Abstract
The vacuum-ultraviolet absorption spectrum of acetaldehyde in the region 180–120 nm has been measured at high resolution. Analysis of the Rydberg series determines a value of the ionisation potential to be 82 526.45 ± 0.05 cm–1, the high accuracy resulting from one series that is observed to n= 45. Rydberg series of s, p and d type are resolved over a large region of the spectrum, and this is the most extensive large-molecule spectrum ever reported. The spectra of two deuteride derivatives of acetaldehyde are also reported and analysed. These are similar except for significant shifts in the ionisation potential which are shown to be consistent with zero-point energy effects. The very long series is of p-type and is not predissociated throughout the entire spectrum. Explaining this requires consideration of the location of the origin of the Rydberg orbitals and their orientation with respect to the bonds in the molecule. Such consideration of location, distribution and orientation of molecular Rydberg orbitals is novel and may be of general applicability.
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