Experimental and Theoretical Studies of Photoionization-Efficiency Curves for C2H2 and C2D2

Abstract

Photoionization-efficiency curves for C2H2 and C2D2 have been remeasured in the wavelength region from onset of ionization to 600 Å, using a gold-coated grating and the Hopfield continuum as a photon source. The curve shapes of the molecule ions near threshold are compared with calculations of the Franck—Condon factors. Nearly exact agreement between experiment and calculation is obtained when taking into account hot bands. A general discussion is given for the shape of the molecule-ion curve and for that of the fragment ions, C2H+ and C2D+. The observed onsets of ionization for the latter ions are 17.22— and 17.34 eV, respectively.

Calculated Vibrational Intensities in the ÖX̃ Electronic Transition of Acetylene

“…These results agree with the corrected version of the equation of Sharp and Rosenstock (45,46) and with the generating function, Eq. (4.1), of Doktorov et al (47).…”

A general time-dependent route to Resonance-Raman spectroscopy including Franck-Condon, Herzberg-Teller and Duschinsky effects

“…These integrals can be computed with a TI formulation, using the same metodology as for vibronic spectroscopy 11,12 . Analytic formulae have been derived, first explicitly for each transitions 13,14 and later for series of transitions based on the number of simultaneously excited oscillators in the initial and final states 15,16 . However, they remain not general enough to be applicable to complex and large systems.…”

The outer valence photoionization of acetylene

“…37 Since acetylene dissociatively ionizes to form C 2 H ϩ and H at ϳ17.2 eV, it would be a likely candidate for this behavior. 8,13 Further, there is a dip in the photoionization quantum yield that is roughly centered at the photon energy region where Avaldi et al data exhibits the most intense features in region II, and this dip indicates the presence of competing dissociative processes. 3 However, photoion-photoelectron coincidence spectra do not support this supposition.…”

“…1 One example of this occurs with photoionization into the X 2 ⌸ u state of acetylene; experimental results for this system in the ϳ11.4-16.6 eV photon energy region reveal a complicated structure, about which there has existed a long-standing controversy concerning the exact assignment of experimentally observed structures and the attendant dynamics of photoionization giving rise to same. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Concurrent with this experimentally driven controversy, there has been a significant amount of theoretical work. 2,11,12,[16][17][18][19] The theoretical work to date has contributed much to clarify the situation, but so far has not resolved all issues.…”