EXPLORING THE CH STRETCH SPECTRAL REGION OF CRYPTAND/ION COMPLEXES WITH IR-UV DOUBLE RESONANCE SPECTROSCOPY AND LOCAL MODE HAMILTONIANS

Sibert, Edwin

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Title

EXPLORING THE CH STRETCH SPECTRAL REGION OF CRYPTAND/ION COMPLEXES WITH IR-UV DOUBLE RESONANCE SPECTROSCOPY AND LOCAL MODE HAMILTONIANS

Author(s)

Sibert, Edwin

Contributor(s)

• Zwier, Timothy S.
• Au, Kendrew
• Foley, Casey Daniel

Issue Date

2023-06-20

Keyword(s)

Mini-symposium: Spectroscopy with Cryogenic Ion Traps

Abstract

The infrared spectroscopy of cryptands containing Na⁺, K⁺, Rb⁺, Sr²⁺, and Ba²⁺ ions are studied both theoretically and experimentally. Specifically, [2, 2, 2] cryptand complexes are modified to contain a phenyl group as shown below. The complexes are formed in solution and brought into the gas phase by electrospray methods. After mass selection, the complexes are introduced into a cryo-cooled octupole ion trap and cooled to 5 K. The aromatic chromophore in the crypt provides a UV absorption that is used to record a UV photofragment spectrum that shifts to unique wavelengths depending on the size and charge of the embedded ion. Infrared spectra in the alkyl CH stretch region are recorded using IR-UV double resonance. The UV wavelength is fixed on the S₀-S₁ origin of the complex, while a tunable IR laser records the IR spectrum in the ground electronic state by depleting the photofragment ion signal. The resulting spectra are investigated theoretically by first searching for low-lying conformers and subsequently modeling the CH stretch fundamentals of these conformers with local mode Hamiltonians which include anharmonic coupling between CH stretches and nearby background states. In contrast to our previous work on alkanes, the ethoxy bridges enhance both CH₂ scissor and wag vibrational frequencies, with the result that scissor overtones and combination bands are detuned from the CH stretch vibrations. The increase in the wag frequencies leads to these modes playing a significant role in the spectral patterns of the CH stretch spectral region. These spectra are used to identify those conformers that are observed experimentally and to explore the role of the central ion’s size in altering the structure of the crypt and, consequently, the peak patterns in the CH stretch spectral region.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122474

DOI

https://doi.org/10.15278/isms.2023.6793

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