Jet-cooled rovibrational spectroscopy of methoxyphenols using two complementary FTIR and QCL based spectrometers

Abstract

Methoxyphenols (MP) are a significant component of biomass burning emissions which mainly exists in our atmosphere in the gas phase where they contribute to the formation of secondary organic aerosols (SOA). Rovibrational spectroscopy is a promising tool to monitor atmospheric MPs and infer their role in SOAs formation. In this study, we bring a new perspective on the rovibrational analysis of MP isomers by taking advantage of two complementary devices combining jet-cooled environments and absorption spectroscopy: the Jet-AILES and the SPIRALES setups. Based on Q-branches frequency positions measured in the Jet-AILES FTIR spectra and guided by quantum chemistry calculations, we propose an extended vibrational and conformational analysis of the different MP isomers in their fingerprint region. Some modes such as far-IR out-of-plane-OH bending or mid-IR in-plane-CH bending allow to assign individually all the stable conformers. Finally, using the SPIRALES setup with three different EC-QCL sources centered on the 930-990 cm −1 and the 1580-1690 cm −1 ranges, it was possible to proceed to the rovibrational analysis of the ν 18 ring in-plane bending mode of the MP meta isomer providing a set of reliable excited state parameters which confirms the correct assignment of two conformers. Interestingly, the observation of broad Q-branches without visible P-and R-branches in the region of the CC ring stretching bands was interpreted as being probably due to a vibrational perturbation. These results highlight the complementarity of broadband FTIR and narrowband laser spectroscopic techniques to reveal the vibrational conformational signatures of atmospheric compounds over a large infrared spectral range.

Intramolecular H-Bond Dynamics of Catechol Investigated by THz High-Resolution Spectroscopy of Its Low-Frequency Modes

“…Compared to the mid-IR, the far-IR spectroscopy allows exploration of the dynamics of low-energy vibrations involving the full molecular backbone. That explains why far-IR/THz high-resolution spectroscopy is so efficient in discriminating subtle structural differences in particular in aromatic compounds (stable conformers [5], isomers [6], etc. ).…”

2-Methoxyethanol: harmonic tricks, anharmonic challenges and chirality-sensitive chain aggregation

“…Other than for successive recording, the simultaneous detection ensures that both spectra obtained are recorded at exactly the same experimental conditions. In contrast to other sequential 13 or simultaneous spectroscopy schemes, 14 the same light source and the same light collection is used, making alignment inside the vacuum chamber somewhat easier. An elegant, but somewhat less flexible alternative would be to use the same optical grating but to collect the Raman scattering in different diffraction orders.…”

Interleaved electro-optic dual comb generation to expand bandwidth and scan rate for molecular spectroscopy and dynamics studies near 1.6 µm

“…For example, standoff methods for remote sensing of greenhouse gases (GHGs) in the atmosphere including differential absorption LIDAR (DIAL) [27,28] and natural target integrated path differential absorption LIDAR (IPDA) [29,30] typically require photomultipliers or avalanche photodiodes [31,32] to detect faint backscattered returns and therefore, require high power per comb tooth over bandwidths of (2-5) cm -1 and at comb resolutions from 100 MHz to 250 MHz [33]. Single quantum level studies of molecules prepared in cold environments also require (2-5) cm -1 of spectral coverage to investigate a single rovibrational [34] or rovibronic band [35,36,37] but with sub-MHz resolution. Under these conditions, achieving the highest signal-to-noise ratio for a given source power and measurement time requires limiting the bandwidth coverage.…”