ELECTRONIC STRUCTURE OF PROTOTYPICAL π- and σ-RADICALS: HYPERFINE-RESOLVED ROTATIONAL SPECTROSCOPY OF PROPARGYL AND PHENYL

Changala, Bryan

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Description

Title

ELECTRONIC STRUCTURE OF PROTOTYPICAL π- and σ-RADICALS: HYPERFINE-RESOLVED ROTATIONAL SPECTROSCOPY OF PROPARGYL AND PHENYL

Author(s)

Changala, Bryan

Contributor(s)

• McCarthy, Michael C
• Ellison, Barney
• Stanton, John F.
• Franke, Peter R.

Issue Date

2023-06-20

Keyword(s)

Radicals

Abstract

The reactivity of hydrocarbon radicals is strongly influenced by the orbital character and distribution of the unpaired electron. Hyperfine-resolved microwave spectroscopy is an ideal tool for measuring this structure in isolated, gas-phase molecules, providing fundamental insights into their open-shell electronic properties and chemical structure. We present examples of this approach applied to two prototypical reactive species: propargyl (HCCCH₂), the smallest resonance-stabilized π-radical, and phenyl (c-C₆H₅), the simplest aryl σ-radical. Using cavity Fourier transform microwave measurements of isotopically substituted propargyl, combined with highly accurate ab initio rovibrational corrections, we have derived its complete semi-experimental equilibrium structure and unpaired spin distribution, which provide vivid, complementary illustrations of π-electron delocalization. Our parallel work on phenyl has focused on the complete assignment of the complex hyperfine structure associated with its five ¹H nuclear spins. In addition to characterizing the singly occupied, carbon-centered σ-orbital, the precisely determined hyperfine parameters enable us to generate a kHz-accuracy cm-wave catalog. These laboratory data are an essential prerequisite for a sensitive astronomical search for phenyl in radio surveys of narrow-linewidth interstellar objects such as cold, dark molecular clouds, where phenyl is thought to be a critical intermediate in the formation of the first aromatic ring. Our work suggests that other large, weakly polar, open-shell hydrocarbons, including benzyl and indenyl, may be amenable to high-resolution microwave characterization.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122340

DOI

https://doi.org/10.15278/isms.2023.6879

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