Photoions produced in methanol and formaldehyde by radiation in the spectral region 450 - 1150 Å were analyzed mass spectrometrically and their relative yields were determined as a function of wavelength. First ionisation potentials were determined and the ion yield curves were interpreted in terms of ionisation processes in conjunction with other data. Fragment ions were detected on mass numbers 31, 30, 29, 15, and 14 for methanol, and 29, 2, and 1 for formaldehyde. The associated appearence potentials were determined and were used to calculate heats of formation of the ions CH2OH+ and HCO+, and the radicals CH3, CH2, and HCO. The most important result appears to be the heat of formation found for HCO: ΔHB = 0.43 ± 0.07 eV, corresponding to 9.9 ± 1.6 kcal/mole, as well as the associated dissociation energies for HCO and formaldehyde. Previously existing discrepancies concerning these quantities are thereby clarified
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