Carbon-centered radicals with a hydroperoxy (-OOH) group, commonly known as ·QOOH, are a rarely observed, yet critical intermediate species in hydrocarbon oxidation processes relevant to atmospheric and combustion chemistry. ·QOOH intermediates are the ‘central switchyard’ in the oxidation mechanism, controlling the branching between unimolecular decay to hydroxyl (OH) radical and cyclic ether products or, alternatively, O₂ addition leading to extremely low-volatility organic compounds or fuel autoignition. Prototypical ·QOOH intermediates in the oxidation of isobutane and cyclohexane are directly characterized through their infrared fingerprint involving CH and OH stretch vibrations in the 3500-7000 cm⁻¹ region. Infrared activation also initiates the energy-resolved and time-dependent unimolecular decay of the ·QOOH intermediates to OH radical products. The experiments are complemented by theoretical analyses based on state-of-the-art electronic structure characterization of the transition state barrier regions. The experimental and theoretical studies reveal the dynamical reaction pathways including heavy atom tunneling under controlled laboratory conditions as well as their impact in realistic atmospheric and combustion chemistry.

l0pt Figure I present several problems in chemistry for which molecular structure fine details are relevant to understand the usually complex underlying mechanisms that operate. These systems span areas of chemistry and related areas such as biosciences, astrophysics, materials science and technology. We exploited an experimental strategy which combines microwave and laser spectroscopies in high resolution, NMR, computation and synthesis. Laser spectroscopy offers high sensitivity and selectivity, making it ideal for studying biochemical systems of medium-large size.Cocinero, E. J.; Carcabal, P.; Vaden, T. D.; Simons, J. P. and Davis, B. G., Nature, 469, 76-79, 2011.^,Bermejo, I. A.; Usabiaga, I.; Compañón, I.; Castro−López, J.; Insausti, A.; Fernández, J. A.; Avenoza, A.; Busto, J. H.; Jiménez−Barbero, J.; Asensio, J. L.; Peregrina, J. M.; Jiménez−Osés, G.; Hurtado−Guerrero, R.; Cocinero, E. J. and Corzana, F., J. Am. Chem. Soc. 140, 9952–9960, 2018.oreover, microwave spectroscopy provides higher resolution and direct access to molecular structure.Calabrese, C; Uriarte, I.; Insausti, A.; Vallejo−López, M.; Basterretxea, F. J.; Cochrane, S. A.; Davis, B. G.; Corzana, F. and Cocinero, E. J., ACS Cent. Sci., 6, 293−303, 2020.^,Calabrese, C.; Temelso, B.; Usabiaga, I.; Seifert, N. A.; Basterretxea, F. J.; Prampolini, G.; Shields, G. C.; Pate, B. H.; Evangelisti, L. and Cocinero, E. J., Angew. Chem. Int. Ed. 60, 16894-16899, 2021.his combined approach provides not only accurate chemical insight on conformation, structure and molecular properties, but also benchmarking standards guiding the development of theoretical calculations.

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Footnotes:

Cocinero, E. J.; Carcabal, P.; Vaden, T. D.; Simons, J. P. and Davis, B. G., Nature, 469, 76-79, 2011.\end Bermejo, I. A.; Usabiaga, I.; Compañón, I.; Castro−López, J.; Insausti, A.; Fernández, J. A.; Avenoza, A.; Busto, J. H.; Jiménez−Barbero, J.; Asensio, J. L.; Peregrina, J. M.; Jiménez−Osés, G.; Hurtado−Guerrero, R.; Cocinero, E. J. and Corzana, F., J. Am. Chem. Soc. 140, 9952–9960, 2018.M\end Calabrese, C; Uriarte, I.; Insausti, A.; Vallejo−López, M.; Basterretxea, F. J.; Cochrane, S. A.; Davis, B. G.; Corzana, F. and Cocinero, E. J., ACS Cent. Sci., 6, 293−303, 2020. Calabrese, C.; Temelso, B.; Usabiaga, I.; Seifert, N. A.; Basterretxea, F. J.; Prampolini, G.; Shields, G. C.; Pate, B. H.; Evangelisti, L. and Cocinero, E. J., Angew. Chem. Int. Ed. 60, 16894-16899, 2021.T

Chirality is ubiquitous in nature, and scientists seek to explore this property to better understand life processes and facilitate more efficient chemical processes. Chiroptical studies of molecular chirality in the gas phase are often limited due to weak chiral light-matter interactions. However, a relatively new chiroptical technique, known as photoelectron circular dichroism (PECD), bypasses these weak interactions to enable chiral discrimination measurements with chiral sensitivity that well exceeds conventional techniques such as absorption circular dichroism. This chiroptical effect manifests in the photoemission of electrons from a chiral target, upon irradiation with circularly polarized light. Although there are numerous observations of this effect in the photoionization of neutral chiral molecules, there are minimal known cases of PECD in chiral anions. I will discuss our observation of photoelectron circular dichroism in the photodetachment of anions. In this discussion, I will explain the implications of this result for understanding the universal dynamics that govern this chiroptical effect.

Electro-optic frequency combs possess a unique combination of frequency agility, flexibility, and mutual coherence. Here I will describe a variety of approaches for the generation of electro-optic combs including the use of tailored chirp waveforms produced by low-cost electronics. In addition, I will highlight our recent work in the area of integrated photonics, where the use of nanofabricated electro-optic modulators allows for comb generation and application on chip. Finally, I will discuss the use of electro-optic combs with non-linear spectral translation. This work has led to the generation of frequency agile combs in the mid-infrared, allowing for spectral measurements at timescales as short as 20 ns. In addition, these approaches have been applied in the near-infrared, where nonlinear nanophotonics allows for spectral translation throughout much of the visible and near-infrared with sufficient accuracy to enable applications in quantum sensing and atomic spectroscopy.