Photo-chemical reactions in commercial poly(oxymethylene)

Poly(oxymethylene) has been examined using infra-red, ultraviolet absorption and luminescence techniques. The first technique indicates that aldehydic carbonyl groups are present in the polymer whereas the latter two indicate the presence of α,β-unsaturated carbonyl groups. The behaviour of these impurity carbonyl species during irradiation under sunlight-simulated conditions has also been examined. Possible mechanisms for the participation of these chromophoric units in the photo-oxidation of the polymer are discussed.     

The far-infrared spectrum of acrolein, CH2CHCHO: The ν18 fundamental and (ν17 + ν18) − ν18 hot bands

The ν₁₈ fundamental band (∼158 cm⁻¹) of acrolein is studied at high resolution (0.0015 cm⁻¹) using synchrotron radiation from the Canadian Light Source facility and a Bruker IFS 125HR Fourier transform spectrometer. By fitting this band, together with some pure rotational transitions, molecular parameters are obtained to accurately determine the energies of the ν₁₈ = 1 state levels for values of (J, K_a) up to at least (45, 24). These parameters should be useful for future high resolution studies of acrolein hot bands. This is demonstrated here by a detailed analysis of the (ν₁₇ + ν₁₈) − ν₁₈ hot band at ∼589 cm⁻¹. The upper state (ν₁₇ + ν₁₈) of this band is found to be perturbed by Coriolis interactions analogous to those affecting the ν₁₇ state.     

Line profile study of transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide perturbed by air

In this work we present a line profile study for air-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra were recorded at a resolution of 0.008 cm⁻¹ using a Fourier Transform spectrometer. The air-broadening, air-shift, and air-line mixing coefficients were derived from a simultaneous fitting of spectra using the Voigt model and a Speed-Dependent Voigt lineshape model. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.     

A compact automatic wavemeter for use with tunable infrared diode lasers

We have studied the magnetic-dipole and electric-quadrupole contributions to second-harmonic generation (SHG) of centro-symmetric media. It can be shown that the phenomenological parameters , , can be arranged to form an effective -tensor, which describes dipole-forbidden SHG as the effect of a surface layer upon excitation with a single plane electromagnetic wave. An experimental technique is proposed allowing a determination of the usually very small term due to magnetic-dipole interaction using coherent compensation of its contribution by a coverage with an appropriate dye monolayer.     

THE FLAVIN SENSITISED PHOTOOXIDATION OF ASCORBIC ACID: A CONTINUOUS AND FLASH PHOTOLYSIS STUDY

Abstract —The mechanism of the photooxidation of ascorbic acid by flavin mononucleotide has been studied by steady state and flash photolysis techniques. The primary reaction consists of an electron abstraction from ascorbic acid by the flavin singlet and triplet states by a diffusional process and in the latter case also by the formation of a triplet flavin-ascorbic acid complex. Under anaerobic conditions, the secondary reactions consist primarily of a radical recombination and a 'dark'chemical back reaction, leading to the reformation of unchanged flavin and ascorbic acid. In the presence of oxygen, the 'back reactions'are prevented, resulting in the efficient photooxidation of ascorbic acid.