HIGH-RESOLUTION, JET-COOLED INFRARED SPECTROSCOPY OF TRANS-FORMIC ACID: ANALYSIS OF ν₁ OH STRETCHING FUNDAMENTAL

Chan, Ya-Chu

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Title

HIGH-RESOLUTION, JET-COOLED INFRARED SPECTROSCOPY OF TRANS-FORMIC ACID: ANALYSIS OF ν₁ OH STRETCHING FUNDAMENTAL

Author(s)

Chan, Ya-Chu

Contributor(s)

Nesbitt, David

Issue Date

2023-06-20

Keyword(s)

Small molecules

Abstract

High-resolution infrared reduced-Doppler absorption spectra of jet-cooled gas phase trans-formic acid at Trₒt ≈ 10.9(5) K are reported for the first time in the ν₁ OH stretching fundamental region, obtained by supersonically expanding trans-formic acid/Ar mixtures through a slit jet nozzle source. Four rovibrational bands are observed, with origins at 3570.493(5) (a/b-type), 3566.793(5) (a/b-type), 3560.032(9) (b-type), and 3534.6869(2) (a-type) cm−¹, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibertᵃ, these four bands have been assigned to ν₁, ν₂ + ν₇, ν₆ + 2ν₇ + 2ν₉ (tentatively by our work), and 2ν₃, respectively. Specifically, two of the three upper dark states 2¹7¹ (a′) and 6¹7²9² (a′) are close enough to the “bright” 1¹ (a′) state to facilitate strong anharmonic resonance interactions, resulting in intensity mixing into the two zero-order bands that would otherwise be “dark”. Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between zero-order 1¹ and 2¹7¹ states. This motivates the development of a 3 coupled state (1¹, 2¹7¹, and 6¹7²9²) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate coupling. Though limited by the range of J and Kₐ levels (J′ ≤ 9 and Kₐ′ ≤ 3) populated at supersonic jet temperatures, this work offers the first precision spectroscopic analysis of trans-formic acid in the ν₁ OH stretching region, which should aid in the assignment of the more complete yet highly congested room temperature FTIR spectraᵇ.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122460

DOI

https://doi.org/10.15278/isms.2023.6770

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