Browsing by Author "Franke, Peter R."

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Infrared spectroscopy of propene in solid para-hydrogen and helium droplets: The role of matrix shifts in the analysis of anharmonic resonances
(2018-12-01)
Pullen, Gregory T.
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Franke, Peter R.
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Lee, Yuan-Pern
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Douberly, Gary E.
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The infrared spectrum of propene in the CH stretching region is complicated by anharmonic resonance polyads associated with the coupling of CH stretch fundamentals to overtones and combinations of CH, bends and CC stretches. We report the spectra of propene isolated in both helium nanodroplets (HENDI) and solid para-hydrogen (p-H-2). Spectral assignments and anharmonic polyad memberships are obtained with a VPT2+K effective Hamiltonian. In the 2800-3120 cm(-1) region, the average differential matrix shift in going from HENDI to p-H-2 is similar to 4.4 cm(-1) to the red, with a standard deviation of 1.9 cm(-1). Moreover, the choice of matrix environment influences the positions and intensity ratios of transitions within the resonance polyads. Two-state interaction models are used to confirm that differential matrix shifts less than 10 cm(-1) are sufficient to account for the observed differences. (C) 2018 Elsevier Inc. All rights reserved.
Infrared spectroscopy of the n-propyl and i-propyl radicals in solid para-hydrogen
(2019-09-01)
Pullen, Gregory T.
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Franke, Peter R.
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Haupa, Karolina A.
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Lee, Yuan-Pern
;
Douberly, Gary E.
We report infrared spectra of the n- and i-propyl radicals isolated in solid para-hydrogen (p-H-2). Propyl radicals were produced via 248 nm irradiation of matrices formed by co-deposition of p-H-2 and either 1-iodopropane (forming n-propyl) or 2-iodopropane (forming i-propyl). Secondary photolysis was used to group spectral bands arising from the same species. In addition to those observed previously in either argon matrix or helium droplet spectra, we assign approximately 20 previously unreported bands. The assignment of features to propyl radicals is made via comparisons to VPT2+K anharmonic frequency computations. In separate measurements, propyl radicals were generated via the reaction between propene and hydrogen atoms produced within the p-H-2 matrix. Because the barriers are between 700 and 1500 cm(-1), the H + propene reaction is necessarily under tunneling control when carried out in solid p-H-2 at 3.3 K. i-Propyl radicals were produced in similar to 5-20 times greater abundance than n-propyl radicals, indicating that H atom addition to the terminal carbon is faster than addition to the central carbon. The Wentzl-Kramers-Brillouin approximation is applied to one-dimensional ab initio potentials to estimate the tunneling time constants for formation of n- and i-propyl. This model predicts the rate of addition to the terminal carbon (forming i-propyl) to be 17 times faster, in qualitative agreement with the experimental branching ratio. (C) 2019 Elsevier Inc. All rights reserved.