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Matrix-formation dynamics dictate methyl nitrite conformer abundance.

Emily K Hockey¹, Nathan McLane², Korina Vlahos¹

¹Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.

The Journal of Chemical Physics

|March 4, 2024

Summary

The conformational abundance of methyl nitrite (CH3ONO) changes upon deposition onto cold substrates, contrary to gas-phase expectations. Surface properties of the growing matrix influence conformer trapping, favoring the cis isomer.

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Area of Science:

Physical Chemistry
Spectroscopy
Quantum Chemistry

Background:

Methyl nitrite (CH3ONO) exists as two stable conformers: cis and trans.
Interconversion between cis and trans methyl nitrite is hindered by a high rotational barrier.
Matrix-isolated conformer abundance is typically assumed to reflect gas-phase populations.

Purpose of the Study:

To investigate the influence of deposition conditions on methyl nitrite conformer abundance.
To determine if matrix surface properties affect conformer populations.
To challenge the assumption that matrix-isolated conformer abundance mirrors gas-phase abundance.

Main Methods:

In situ infrared spectroscopy to measure conformer abundance.
Deposition of methyl nitrite onto cold substrates with varying bath gases (N2, Ar, Xe) and angles.
Quantum chemistry calculations of binding energies for CH3ONO-bath gas complexes.

Main Results:

The relative abundance of the cis methyl nitrite conformer increases upon deposition compared to its gas-phase population.
Conformer abundance varies with the identity of the bath gas and deposition angle.
No significant energetic stabilization was found in 1:1 complexes of CH3ONO with N2, Ar, or Xe.

Conclusions:

The growing matrix surface significantly influences the trapping of methyl nitrite conformers.
The cis conformer is preferentially trapped, likely due to its more compact structure.
Careful characterization of conformers in matrix-isolated systems is crucial, necessitating further study of deposition dynamics and surface structures.