Resonance effects in elastic cross sections for electron scattering on pyrimidine: Experiment and theory

Journal Article · Fri Jan 08 00:00:00 EST 2016 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4937790· OSTI ID:1468475

Regeta, Khrystyna ^[1]; Allan, Michael  ^[1]; Winstead, Carl  ^[2]; McKoy, Vincent ^[2]; Mašín, Zdeněk ^[3]; Gorfinkiel, Jimena D. ^[4]

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1. Univ. of Fribourg, Fribourg (Switzerland)
2. California Inst. of Technology (CalTech), Pasadena, CA (United States)
3. Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Berlin (Germany)
4. The Open Univ., Milton Keynes (United Kingdom)

Here, we measured differential cross sections for elastic (rotationally integrated) electron scattering on pyrimidine, both as a function of angle up to 180° at electron energies of 1, 5, 10, and 20 eV and as a function of electron energy in the range 0.1–14 eV. The experimental results are compared to the results of the fixed-nuclei Schwinger variational and R-matrix theoretical methods, which reproduce satisfactorily the magnitudes and shapes of the experimental cross sections. The emphasis of the present work is on recording detailed excitation functions revealing resonances in the excitation process. Resonant structures are observed at 0.2, 0.7, and 4.35 eV and calculations for different symmetries confirm their assignment as the $$\sim\atop{\chi}$$²A₂, $$\sim\atop{A}$$²B₁, and $$\sim\atop{B}$$²B₁ shape resonances. As a consequence of superposition of coherent resonant amplitudes with background scattering the $$\sim\atop{B}$$²B₁ shape resonance appears as a peak, a dip, or a step function in the cross sections recorded as a function of energy at different scattering angles and this effect is satisfactorily reproduced by theory. The dip and peak contributions at different scattering angles partially compensate, making the resonance nearly invisible in the integral cross section. Vibrationally integrated cross sections were also measured at 1, 5, 10 and 20 eV and the question of whether the fixed-nuclei cross sections should be compared to vibrationally elastic or vibrationally integrated cross section is discussed.

• Research Organization: California Institute of Technology (CalTech), Pasadena, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
• Grant/Contract Number: FG02-97ER14814
• OSTI ID: 1468475
• Alternate ID(s): OSTI ID: 1234269
• Journal Information: Journal of Chemical Physics, Vol. 144, Issue 2; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY