Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH2Br2 in the 2960 to 3120 cm−1 region

Ibrahim Sadiek; Adrian Hjältén; Frances C. Roberts; Julia H. Lehman; Aleksandra Foltynowicz

doi:10.1039/d2cp05881b

Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH₂Br₂ in the 2960 to 3120 cm⁻¹ region

Ibrahim Sadiek^*, Adrian Hjältén, Frances C. Roberts, Julia H. Lehman, Aleksandra Foltynowicz

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

2 Citations (Scopus)

66 Downloads (Pure)

Abstract

Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH₂Br₂, from 2960 cm⁻¹ to 3120 cm⁻¹ by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH₂⁸¹Br₂, CH₂⁷⁹Br⁸¹Br, and CH₂⁷⁹Br₂, are assigned. These four vibrational transitions are attributed to the fundamental ν₆ band and the nearby nν₄ + ν₆ − nν₄ hot bands (with n = 1-3) due to the population of the low-lying ν₄ mode of the Br-C-Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong Q_{K_a}(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm⁻¹. A detailed fit of the ν₆ band of the CH₂⁷⁹Br⁸¹Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm^-1.

Original language	English
Pages (from-to)	8743-8754
Number of pages	12
Journal	Physical Chemistry Chemical Physics
Volume	25
Issue number	12
Early online date	14 Feb 2023
DOIs	https://doi.org/10.1039/d2cp05881b
Publication status	Published - 28 Mar 2023

Bibliographical note

Funding Information:
The work at the University of Leeds was supported by funding from the EPSRC (Grant No. EP/R01518X/1 and EP/R513258/1). The work at Umeå University was supported by funding from the Knut and Alice Wallenberg Foundation (KAW 2015.0159 and 2020.0303) and the Swedish Research Council (2016-03593 and 2020-00238). Computational support was enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. Some of the computational work was also undertaken on ARC3, part of the High Performance Computing facilities at the University of Leeds, UK. I. Sadiek would like to thank the German Research Foundation for financing his current position at the INP (SA 4483/1-1). The authors would like to acknowledge the help of A. Downing, and the fruitful discussions with G. Friedrichs, K. K. Lehmann, and the late C. Western.

Publisher Copyright:
© 2023 The Royal Society of Chemistry

ASJC Scopus subject areas

General Physics and Astronomy
Physical and Theoretical Chemistry

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Cite this

@article{a65efaf5103f484f8a29b6968ea4944d,

title = "Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH2Br2 in the 2960 to 3120 cm−1 region",

abstract = "Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH2Br2, from 2960 cm−1 to 3120 cm−1 by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH281Br2, CH279Br81Br, and CH279Br2, are assigned. These four vibrational transitions are attributed to the fundamental ν6 band and the nearby nν4 + ν6 − nν4 hot bands (with n = 1-3) due to the population of the low-lying ν4 mode of the Br-C-Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong QKa(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm−1. A detailed fit of the ν6 band of the CH279Br81Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm-1.",

author = "Ibrahim Sadiek and Adrian Hj{\"a}lt{\'e}n and Roberts, {Frances C.} and Lehman, {Julia H.} and Aleksandra Foltynowicz",

note = "Funding Information: The work at the University of Leeds was supported by funding from the EPSRC (Grant No. EP/R01518X/1 and EP/R513258/1). The work at Ume{\aa} University was supported by funding from the Knut and Alice Wallenberg Foundation (KAW 2015.0159 and 2020.0303) and the Swedish Research Council (2016-03593 and 2020-00238). Computational support was enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. Some of the computational work was also undertaken on ARC3, part of the High Performance Computing facilities at the University of Leeds, UK. I. Sadiek would like to thank the German Research Foundation for financing his current position at the INP (SA 4483/1-1). The authors would like to acknowledge the help of A. Downing, and the fruitful discussions with G. Friedrichs, K. K. Lehmann, and the late C. Western. Publisher Copyright: {\textcopyright} 2023 The Royal Society of Chemistry",

year = "2023",

month = mar,

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doi = "10.1039/d2cp05881b",

language = "English",

volume = "25",

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T1 - Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH2Br2 in the 2960 to 3120 cm−1 region

AU - Sadiek, Ibrahim

AU - Hjältén, Adrian

AU - Roberts, Frances C.

AU - Lehman, Julia H.

AU - Foltynowicz, Aleksandra

N1 - Funding Information: The work at the University of Leeds was supported by funding from the EPSRC (Grant No. EP/R01518X/1 and EP/R513258/1). The work at Umeå University was supported by funding from the Knut and Alice Wallenberg Foundation (KAW 2015.0159 and 2020.0303) and the Swedish Research Council (2016-03593 and 2020-00238). Computational support was enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. Some of the computational work was also undertaken on ARC3, part of the High Performance Computing facilities at the University of Leeds, UK. I. Sadiek would like to thank the German Research Foundation for financing his current position at the INP (SA 4483/1-1). The authors would like to acknowledge the help of A. Downing, and the fruitful discussions with G. Friedrichs, K. K. Lehmann, and the late C. Western. Publisher Copyright: © 2023 The Royal Society of Chemistry

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N2 - Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH2Br2, from 2960 cm−1 to 3120 cm−1 by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH281Br2, CH279Br81Br, and CH279Br2, are assigned. These four vibrational transitions are attributed to the fundamental ν6 band and the nearby nν4 + ν6 − nν4 hot bands (with n = 1-3) due to the population of the low-lying ν4 mode of the Br-C-Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong QKa(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm−1. A detailed fit of the ν6 band of the CH279Br81Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm-1.

AB - Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH2Br2, from 2960 cm−1 to 3120 cm−1 by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH281Br2, CH279Br81Br, and CH279Br2, are assigned. These four vibrational transitions are attributed to the fundamental ν6 band and the nearby nν4 + ν6 − nν4 hot bands (with n = 1-3) due to the population of the low-lying ν4 mode of the Br-C-Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong QKa(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm−1. A detailed fit of the ν6 band of the CH279Br81Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm-1.

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