Absolute photoabsorption and photoionization of formaldehyde in the VUV and soft X-ray regions (3–200 eV) Original Research Article

The absolute photoabsorption spectrum of the valence shell of formaldehyde has been measured using dipole (e,e) spectroscopy from ≈3–200 eV photon energy. Long range absolute oscillator strength (cross section) measurements have been performed at ≈1 eV fwhm resolution, while the low energy discrete structured region (3–20 eV) has been examined in more detail at ≈50 meV fwhm resolution. Absolute oscillator strenghts for many of the individual discrete vibronic transitions have been obtained. In addition, dipole (e,e + ion) coincidence spectroscopy has been used to study the ionic photofragmentation of formaldehyde. Photoion branching ratios, absolute partial photoionization oscillator strenghts and photoionization efficiencies have been obtained from the first IP up to 80 eV photon energy. A dipole induced breakdown scheme for formaldehyde has been derived using the present results in combination with previously published photoelectron-photoion coincidence measurements (R. Bombach et al., Int. J. Mass Spectrum. Ion Phys. 40 (1981) 275) and experimental (D.M.P. Holland, Chem. Phys. 133 (1989) 453) and theoretical (P.W. Langhoff et al., J. Chem. Phys. 69 (1978) 4689) valence shell photoelectron branching ratios. From this breakdown analysis, electronic ion state partial photoionization oscillator strengths for formaldehyde from 14–30 eV photon energy have been derived.