February 2024
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16 Reads
The Journal of Physical Chemistry Letters
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February 2024
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16 Reads
The Journal of Physical Chemistry Letters
September 2022
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17 Reads
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5 Citations
Journal of the American Society for Mass Spectrometry
Decarboxylation of carboxylate ions in the gas phase provides a useful window into the chemistry displayed by these reactive carbanion intermediates. Here, we explore the species generated by decarboxylation of two benzoate derivatives: 2-formylbenzoate (2FBA) and 2-benzoylbenzoate (2BBA). The nascent product anions are transferred to a cryogenic ion trap where they are cooled to ∼15 K and analyzed by their pattern of vibrational bands obtained with IR photodissociation spectroscopy of weakly bound H2 molecules. The structures of the quenched species are then determined by comparison of these spectra with those predicted by electronic structure calculations for local minima on the potential energy surface. The 2-phenide carbanion generated by decarboxylation of 2FBA occurs in two isomeric forms that differ in the orientation of the formyl group, both of which yield a very large (∼110 cm-1) redshift in the stretching frequency of the H2 molecule attached to the anionic carbon center. Although calculated to be a local minimum, the analogous 2-phenide species could not be isolated upon decarboxylation of 2BBA. Rather, the anionic product adopts a ring-closed structure, indicating efficient nucleophilic attack on the pendant phenyl group by the nascent phenide. The barrier for ring closing is evaluated with electronic structure calculations.
June 2022
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16 Reads
June 2022
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20 Reads
March 2022
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42 Reads
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9 Citations
The Journal of Physical Chemistry Letters
June 2021
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9 Reads
September 2020
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62 Reads
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14 Citations
The Journal of Physical Chemistry A
CN is known for its fast reactions with hydrocarbons at low temperatures, but relatively few studies have focused on the reactions between CN and aromatic molecules. The recent detection of benzonitrile in the interstellar medium, believed to be produced by the reaction of CN and benzene, has ignited interest in studying these reactions. Here, we report rate constants of the CN + toluene (C7H8) reaction between 15 and 294 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme; reaction kinetics in uniform supersonic flow) apparatus coupled with the pulsed laser photolysis - laser induced fluorescence (PLP-LIF) technique. We also present the stationary points on the potential energy surface of this reaction to study the available reaction pathways. We find the rate constant does not change over this temperature range, with an average value of (4.1 ± 0.2) × 10-10 cm3 s-1, which is notably faster than the only previous measurement at 105 K. While the reason for this disagreement is unknown, we discuss the possibility that it is related to enhanced multiphoton effects in the previous work.
June 2020
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14 Reads
June 2020
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14 Reads
March 2020
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41 Reads
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65 Citations
The Astrophysical Journal Letters
The low-temperature reaction between CN and benzene (C 6 H 6 ) is of significant interest in the astrochemical community due to the recent detection of benzonitrile, the first aromatic molecule identified in the interstellar medium (ISM) using radio astronomy. Benzonitrile is suggested to be a low-temperature proxy for benzene, one of the simplest aromatic molecules, which may be a precursor to polycyclic aromatic hydrocarbons. In order to assess the robustness of benzonitrile as a proxy for benzene, low-temperature kinetics measurements are required to confirm whether the reaction remains rapid at the low gas temperatures found in cold dense clouds. Here, we study the C 6 H 6 + CN reaction in the temperature range 15–295 K, using the well-established CRESU technique (a French acronym standing for Reaction Kinetics in Uniform Supersonic Flow) combined with pulsed-laser photolysis-laser-induced fluorescence. We obtain rate coefficients, k ( T ), in the range (3.6–5.4) × 10 ⁻¹⁰ cm ³ s ⁻¹ with no obvious temperature dependence between 15 and 295 K, confirming that the CN + C 6 H 6 reaction remains rapid at temperatures relevant to the cold ISM.
... Article likely due to oxidation of NA. 20 Yet, a simultaneous growth of a negative absorption band at 1704 cm −1 , also attributed to the stretching mode of C�O functional groups, indicates a loss of mass due to fractionation or decarboxylation of the complex sample, leading to VOC and CO 2 formation. 33,55,56 Slight positive absorptions at 1404 and 1370 cm −1 , corresponding to the bending modes of aldehydic C−H and O−H product functional groups, further support these observations. 20 These simultaneous processes of oxidation and decarboxylation offset one another, resulting in no measurable mass change in the QCM. Figure 7B shows the vibrational spectroscopy results of 1:5 m-DOM/NA thin film, where distinct features of oxygenated product formation are identified. ...
September 2022
Journal of the American Society for Mass Spectrometry
... The importance of halogen bonded complexes have also been reported for the halogen exchange reaction in (HOCl)···(I − ) aq and were explored spectroscopically. 27 Here, with AIMD simulations, we report the microscopic details of Cl 2 formation at acidic pH. Interestingly, under neutral pH condition, although Cl 2 forms transiently, it was not released in the subsequent process. ...
March 2022
The Journal of Physical Chemistry Letters
... The rotational emission from these unambiguously detected PAHs has been observed towards TMC-1 and originates from CN-functionalized PAHs (nitriles), with the exception of the asymmetric, pure PAH indene. It has been proposed that, owing to their large dipole moments, nitrile-substituted PAHs can be used as observational proxies for pure PAHs 23,24 . Extracting quantitative abundances of unsubstituted PAHs from these proxies, however, relies on knowledge of the kinetics of their dominant formation and destruction pathways 25 . ...
September 2020
The Journal of Physical Chemistry A
... 25 Recently, the detection of cyanobenzene and cyanonaphthalene in the molecular cloud TMC-1 via radioastronomy confirms the existence of cyano-substituted PAHs (CN-PAHs), 26,27 molecules where a CN group replaces one of the peripheral hydrogens, in astronomical sources. This, in combination with the launch of JWST, has led to a surge in interest in the spectroscopy of CN-PAHs, [28][29][30][31][32][33][34][35] particularly for the CN stretch region (∼2300 cm −1 ). A few laboratory studies have investigated the absorption spectrum of cyanobenzene, cyanonaphthalene, and cyanoanthracene in Ar-and H 2 O-matrices 36,37 as well as in the gas-phase, 38 but correlation to interstellar environments is left wanting. ...
March 2020
The Astrophysical Journal Letters
... The rotational emission from these unambiguously detected PAHs has been observed towards TMC-1 and originates from CN-functionalized PAHs (nitriles), with the exception of the asymmetric, pure PAH indene. It has been proposed that, owing to their large dipole moments, nitrile-substituted PAHs can be used as observational proxies for pure PAHs 23,24 . Extracting quantitative abundances of unsubstituted PAHs from these proxies, however, relies on knowledge of the kinetics of their dominant formation and destruction pathways 25 . ...
March 2020
The Astrophysical Journal Letters