1
|
Caster KL, Seifert NA, Ruscic B, Jasper AW, Prozument K. Dynamics of HCN, HNC, and HNCO Formation in the 193 nm Photodissociation of Formamide. J Phys Chem A 2024; 128:7761-7771. [PMID: 39225655 DOI: 10.1021/acs.jpca.4c02232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
Formamide (NH2CHO) is the simplest molecule containing a peptide linkage [-NH-C(═O)-], and it plays an essential role in the study of prebiotic chemistry. Exposure to UV irradiation allows formamide to decompose and act as a prebiotic feedstock in the formation of nucleobases and other necessary starting materials. The photodissociation mechanism of gaseous formamide at 193 nm is studied using (a) chirped-pulse Fourier transform millimeter-wave spectroscopy in the 260-290 GHz spectral region in a room-temperature flow-tube reactor at 1 μbar pressure, (b) a combination of electronic structure theory, transition state theory, and quasiclassical trajectories, and (c) the Active Thermochemical Tables. The HCN and HNC photoproducts of hydrogenated (NH2CHO) and deuterated (NH2CDO and ND2CHO) formamide precursors are examined to gain insight into the photodissociation mechanism. The theoretical investigation has characterized the main pathway leading to each of the HCN/HNC isomers from the precursor isotopologues. The theoretical branching ratio [HNC]/[HCN] = 2.1 for nascent photofragments agrees with the experiment. The effect of the postphotolysis HNC ↔ HCN isomerization on the [HNC]/[HCN] ratio is predicted. We report the experimental branching ratio [HNCO]: ([HNC] + [HCN]) = 12 ± 3 and propose that most of HNCO originates from dissociation on the S1 electronic state of formamide.
Collapse
Affiliation(s)
- Kacee L Caster
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Nathan A Seifert
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Department of Chemistry and Chemical & Biomedical Engineering, University of New Haven, West Haven, Connecticut 06516, United States
| | - Branko Ruscic
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Ahren W Jasper
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Kirill Prozument
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| |
Collapse
|
2
|
Guillaume T, Hays BM, Gupta D, Cooke IR, Abdelkader Khedaoui O, Hearne TS, Drissi M, Sims IR. Product-specific reaction kinetics in continuous uniform supersonic flows probed by chirped-pulse microwave spectroscopy. J Chem Phys 2024; 160:204201. [PMID: 38808747 DOI: 10.1063/5.0203428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Accepted: 05/06/2024] [Indexed: 05/30/2024] Open
Abstract
Experimental studies of the products of elementary gas-phase chemical reactions occurring at low temperatures (<50 K) are very scarce, but of importance for fundamental studies of reaction dynamics, comparisons with high-level quantum dynamical calculations, and, in particular, for providing data for the modeling of cold astrophysical environments, such as dense interstellar clouds, the atmospheres of the outer planets, and cometary comae. This study describes the construction and testing of a new apparatus designed to measure product branching fractions of elementary bimolecular gas-phase reactions at low temperatures. It combines chirped-pulse Fourier transform millimeter wave spectroscopy with continuous uniform supersonic flows and high repetition rate laser photolysis. After a comprehensive description of the apparatus, the experimental procedures and data processing protocols used for signal recovery, the capabilities of the instrument are explored by the study of the photodissociation of acrylonitrile and the detection of two of its photoproducts, HC3N and HCN. A description is then given of a study of the reactions of the CN radical with C2H2 at 30 K, detecting the HC3N product, and with C2H6 at 10 K, detecting the HCN product. A calibration of these two products is finally attempted using the photodissociation of acrylonitrile as a reference process. The limitations and possible improvements in the instrument are discussed in conclusion.
Collapse
Affiliation(s)
| | | | | | | | | | | | | | - Ian R Sims
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
- Institut universitaire de France (IUF), France
| |
Collapse
|
3
|
Sun W, Pinacho P, Obenchain DA, Schnell M. Gas-Phase Characterization of Adipic Acid, 6-Hydroxycaproic Acid, and Their Thermal Decomposition Products by Rotational Spectroscopy. J Phys Chem Lett 2024; 15:817-825. [PMID: 38232320 PMCID: PMC10823529 DOI: 10.1021/acs.jpclett.3c02969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 11/29/2023] [Accepted: 11/30/2023] [Indexed: 01/19/2024]
Abstract
We report the spectroscopic investigation of two bifunctional aliphatic carboxylic acids, namely, adipic acid and 6-hydroxycaproic acid, in the gas phase by combining high-resolution rotational spectroscopy and supersonic expansions. Their pure rotational spectra were successfully identified and characterized. However, due to the low thermal stability of these two chemicals, the measured rotational spectra were significantly congested with transitions corresponding to their decomposition products upon heating. We observed cyclopentanone and adipic anhydride in the spectrum of adipic acid and ε-caprolactone and its monohydrate in the spectrum of 6-hydroxycaproic acid. On the basis of the distinct fingerprints of both carboxylic acids and a series of their decomposition products, the spectra were analyzed in a time-segmented manner. This provides valuable insights into the thermal decomposition mechanisms of these two samples over time, which highlights the robustness of microwave spectroscopy as a potent tool for analyzing complex chemical mixtures in a species-, isomer-, and conformer-selective way.
Collapse
Affiliation(s)
- Wenhao Sun
- Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Pablo Pinacho
- Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | | | - Melanie Schnell
- Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
- Institute
of Physical Chemistry, Christian-Albrechts-Universität
zu Kiel, Max-Eyth-Strasse 1, 24118 Kiel, Germany
| |
Collapse
|
4
|
Thawoos S, Suas-David N, Gurusinghe RM, Edlin M, Behzadfar A, Lang J, Suits AG. Low temperature reaction kinetics inside an extended Laval nozzle: REMPI characterization and detection by broadband rotational spectroscopy. J Chem Phys 2023; 159:214201. [PMID: 38054511 DOI: 10.1063/5.0178533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 11/06/2023] [Indexed: 12/07/2023] Open
Abstract
Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20 K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20 K of 6.66 ± 0.47 × 10-11 cm3 molec-1 s-1.
Collapse
Affiliation(s)
- Shameemah Thawoos
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Nicolas Suas-David
- Univ Rennes, CNRS, Institut de Physique de Rennes - UMR 6251, F-35000 Rennes, France
| | - Ranil M Gurusinghe
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
- Department of Chemistry, Tennessee Tech University, Cookeville, Tennessee 38505, USA
| | - Matthew Edlin
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Abbas Behzadfar
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Jinxin Lang
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Arthur G Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| |
Collapse
|
5
|
Zaleski DP, Sivaramakrishnan R, Weller HR, Seifert NA, Bross DH, Ruscic B, Moore KB, Elliott SN, Copan AV, Harding LB, Klippenstein SJ, Field RW, Prozument K. Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm. J Am Chem Soc 2021; 143:3124-3142. [PMID: 33615780 DOI: 10.1021/jacs.0c11677] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH3C(O)CH3) at a nominal temperature of 1800 K. The major product observed is ketene (CH2CO). Minor products identified include acetaldehyde (CH3CHO), propyne (CH3CCH), propene (CH2CHCH3), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.
Collapse
Affiliation(s)
- Daniel P Zaleski
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemistry, Colgate University, Hamilton, New York 13346, United States
| | - Raghu Sivaramakrishnan
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Hailey R Weller
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Nathan A Seifert
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - David H Bross
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Branko Ruscic
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Kevin B Moore
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Sarah N Elliott
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Andreas V Copan
- Emmanuel College, Natural Sciences Department, Franklin Springs, Georgia 30639, United States
| | - Lawrence B Harding
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Stephen J Klippenstein
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Robert W Field
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Kirill Prozument
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| |
Collapse
|
6
|
Photodissociation transition states characterized by chirped pulse millimeter wave spectroscopy. Proc Natl Acad Sci U S A 2020; 117:146-151. [PMID: 31852828 DOI: 10.1073/pnas.1911326116] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The 193-nm photolysis of CH2CHCN illustrates the capability of chirped-pulse Fourier transform millimeter-wave spectroscopy to characterize transition states. We investigate the HCN, HNC photofragments in highly excited vibrational states using both frequency and intensity information. Measured relative intensities of J = 1-0 rotational transition lines yield vibrational-level population distributions (VPD). These VPDs encode the properties of the parent molecule transition state at which the fragment molecule was born. A Poisson distribution formalism, based on the generalized Franck-Condon principle, is proposed as a framework for extracting information about the transition-state structure from the observed VPD. We employ the isotopologue CH2CDCN to disentangle the unimolecular 3-center DCN elimination mechanism from other pathways to HCN. Our experimental results reveal a previously unknown transition state that we tentatively associate with the HCN eliminated via a secondary, bimolecular reaction.
Collapse
|
7
|
Christophe AL, Barnes JT, Twagirayezu S, Mikhonin A, Muckle MT, Neill JL. Direct Measurements of Small Polar Impurities in Gasoline Mixtures Using Molecular Rotational Resonance Spectroscopy. APPLIED SPECTROSCOPY 2019; 73:1334-1339. [PMID: 31219324 DOI: 10.1177/0003702819859012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
This paper reports our efforts to determine whether rotational spectroscopy is a useful tool for petroleum analysis. These efforts include the use of a BrightSpec molecular rotational resonance (MRR) spectrometer, which operates in the 260-290 GHz frequency range, to record rotational spectra of small polar contaminants in commercial gasoline. The observed rotational spectra showed rich, but assignable, patterns due to the sensitivity of the MRR to only small polar compounds. Any interference from a complex hydrocarbon matrix, which in conventional chromatographic methods obscures signals from small polar contaminants, is nearly eliminated. In addition to the evident rotational spectrum of ethanol, the spectra of toluene, ethyl cyanide, and acetaldehyde have also been detected. A quantitative method for ethanol has been developed and demonstrated in this paper, whereas the specific analyses of the other polar impurities will be reported in the future. The validity of MRR to be used as an analytical instrument has been examined by constructing a standard linear curve using dilutions of ethanol in water. The linearity and percentage recovery parameters are satisfactory.
Collapse
Affiliation(s)
| | - Jalon T Barnes
- Department of Chemistry and Biochemistry, Lamar University, Beaumont, TX, USA
| | | | | | | | | |
Collapse
|
8
|
Lou M, Swearer DF, Gottheim S, Phillips DJ, Simmons JG, Halas NJ, Everitt HO. Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:053110. [PMID: 31153269 DOI: 10.1063/1.5093912] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 04/29/2019] [Indexed: 06/09/2023]
Abstract
Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.
Collapse
Affiliation(s)
- Minghe Lou
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
| | - Dayne F Swearer
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
| | - Samuel Gottheim
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
| | - Dane J Phillips
- IERUS Technologies, 2904 Westcorp Blvd., Suite 210, Huntsville, Alabama 35805, USA
| | - Jay G Simmons
- U.S. Army Combat Capabilities Development Command, Aviation and Missile Center, Redstone Arsenal, Alabama 35898, USA
| | - Naomi J Halas
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
| | - Henry O Everitt
- U.S. Army Combat Capabilities Development Command, Aviation and Missile Center, Redstone Arsenal, Alabama 35898, USA
| |
Collapse
|
9
|
Bross DH, Yu HG, Harding LB, Ruscic B. Active Thermochemical Tables: The Partition Function of Hydroxymethyl (CH2OH) Revisited. J Phys Chem A 2019; 123:4212-4231. [DOI: 10.1021/acs.jpca.9b02295] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- David H. Bross
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Hua-Gen Yu
- Division of Chemistry, Department of Energy and Photon Sciences, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Lawrence B. Harding
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Branko Ruscic
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Consortium for Advanced Science and Engineering, The University of Chicago, Chicago, Illinois 60637, United States
| |
Collapse
|
10
|
Feller D, Bross DH, Ruscic B. Enthalpy of Formation of C2H2O4 (Oxalic Acid) from High-Level Calculations and the Active Thermochemical Tables Approach. J Phys Chem A 2019; 123:3481-3496. [DOI: 10.1021/acs.jpca.8b12329] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- David Feller
- Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, United States
| | - David H. Bross
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Branko Ruscic
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
- Consortium for Advanced Science and Engineering, The University of Chicago, Chicago, Illinois 60637, United States
| |
Collapse
|
11
|
Martin-Drumel MA, Baraban JH, Changala PB, Stanton JF, McCarthy MC. The Hunt for Elusive Molecules: Insights from Joint Theoretical and Experimental Investigations. Chemistry 2019; 25:7243-7258. [PMID: 30673130 DOI: 10.1002/chem.201805986] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Indexed: 11/10/2022]
Abstract
Rotational spectroscopy is an invaluable tool to unambiguously determine the molecular structure of a species, and sometimes even to establish its very existence. This article illustrates how experimental and theoretical state-of-the-art tools can be used in tandem to investigate the rotational structure of molecules, with particular emphasis on those that have long remained elusive. The examples of three emblematic species-gauche-butadiene, disilicon carbide, and germanium dicarbide-highlight the close, mutually beneficial interaction between high-level theoretical calculations and sensitive microwave measurements. Prospects to detect other elusive molecules of chemical and astronomical interest are discussed.
Collapse
Affiliation(s)
- Marie-Aline Martin-Drumel
- Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405, Orsay, France
| | - Joshua H Baraban
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel
| | - P Bryan Changala
- JILA, National Institute of Standards and Technology and Department of, Physics, University of Colorado, Boulder, CO, 80309, USA
| | - John F Stanton
- Quantum Theory Project, Departments of Chemistry and Physics, Univ. of Florida, Gainesville, FL, 32611, USA
| | - Michael C McCarthy
- Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, 02138, USA
| |
Collapse
|
12
|
Dias N, Joalland B, Ariyasingha NM, Suits AG, Broderick BM. Direct versus Indirect Photodissociation of Isoxazole from Product Branching: A Chirped-Pulse Fourier Transform mm-Wave Spectroscopy/Pulsed Uniform Flow Investigation. J Phys Chem A 2018; 122:7523-7531. [PMID: 30165738 DOI: 10.1021/acs.jpca.8b04713] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The UV photodissociation of isoxazole (c-C3H3NO) is studied in this work by chirped-pulse Fourier transform mm-wave spectroscopy in a pulsed uniform Laval flow. This approach offers a number of advantages over traditional spectroscopic detection methods due to its broadband, sub-MHz resolution, and fast-acquisition capabilities. In coupling this technique with a quasi-uniform Laval flow, we are able to obtain product branching fractions in the 193 nm photodissociation of isoxazole. Five dissociation channels are explored through direct detection of seven different photoproducts. These species and their respective branching fractions (%) include the following: HCN (53.8 ± 1.7), CH3CN (23.4 ± 6.8), HCO (9.5 ± 2.3), CH2CN (7.8 ± 2.9), CH2CO (3.8 ± 0.9), HCCCN (0.9 ± 0.2), and HNC (0.8 ± 0.2). Guided by previous electronic structure and dynamics simulations, we are able to elucidate the dissociation dynamics that govern the final product branching fractions observed in this work, which differ significantly from previous reports on the thermal decomposition of isoxazole. Interestingly, both direct and indirect dynamics contribute to its dissociation, and clear signatures of both are manifested in the relative branching ratios obtained. Consistent with previous studies on the unimolecular dissociation of isoxazole, our findings also suggest the importance of the open-shell singlet diradicaloid species vinylnitrene in the dissociation dynamics, regardless of the initially populated excited state. This work, taken together with previous investigations, provides a global picture of the complex dissociation pathways involved in the photodissociation of isoxazole.
Collapse
Affiliation(s)
- Nureshan Dias
- Department of Chemistry, University of Missouri , Columbia , Missouri 65211 , United States
| | - Baptiste Joalland
- Department of Chemistry, University of Missouri , Columbia , Missouri 65211 , United States
| | - Nuwandi M Ariyasingha
- Department of Chemistry, University of Missouri , Columbia , Missouri 65211 , United States
| | - Arthur G Suits
- Department of Chemistry, University of Missouri , Columbia , Missouri 65211 , United States
| | - Bernadette M Broderick
- Department of Chemistry, University of Missouri , Columbia , Missouri 65211 , United States
| |
Collapse
|
13
|
Zaleski DP, Prozument K. Automated assignment of rotational spectra using artificial neural networks. J Chem Phys 2018; 149:104106. [DOI: 10.1063/1.5037715] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Daniel P. Zaleski
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439,
USA
| | - Kirill Prozument
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439,
USA
| |
Collapse
|
14
|
Su MD. Photochemical isomerization reactions of acrylonitrile. A mechanistic study. RSC Adv 2018; 8:5647-5651. [PMID: 35539595 PMCID: PMC9078173 DOI: 10.1039/c7ra12614j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 01/29/2018] [Indexed: 11/21/2022] Open
Abstract
The mechanisms for the photochemical isomerization reactions are determined theoretically using the acrylonitrile model molecule. The CASSCF (twelve-electron/eleven-orbital active space) and MP2-CAS methods are respectively used with the 6-311G(d,p) and 6-311++G(3df,3pd) basis sets. The structure of the conical intersection that plays a prominent role in the photoisomerization of acrylonitrile is obtained. The intermediates and the transition structures of the ground states are also calculated, to allow a qualitative explanation of the reaction pathways. These model studies suggest that the preferred reaction route is: acrylonitrile → Franck–Condon region → conical intersection → isoacrylonitrile → transition state → intermediate complex → transition state → cyanoacetylene. The theoretical evidence suggests that conical intersections found in this paper can give a better understanding of the photochemical reactions of acrylonitrile and support the experimental observations. The computational findings indicate that conical intersection plays a central role in understanding the photochemical behaviors of acrylonitrile.![]()
Collapse
Affiliation(s)
- Ming-Der Su
- Department of Applied Chemistry
- National Chiayi University
- Chiayi 60004
- Taiwan
- Department of Medicinal and Applied Chemistry
| |
Collapse
|