CASPT2 Study of the Unimolecular Reactions of Nitromethane—A Look at the Roaming Reactions in the Decomposition of Nitromethane: An Exergonic Route at High Temperatures
Abstract
:1. Introduction
2. Methods of Calculation
Mapping of 2D Potential Energy Surfaces
3. Results and Discussion
3.1. Unimolecular Reactions of Nitromethane and Methyl Nitrite
3.2. A Look at the So-Called Loose Transition State
4. Conclusions
Supplementary Materials
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
- Word, M.D.; Lo, H.A.; Boateng, D.A.; McPherson, S.L.; Gutsev, G.L.; Gutsev, L.G.; Lao, K.U.; Tibbetts, K.M. Ultrafast dynamics of nitro–nitrite rearrangement and dissociation in nitromethane cation. J. Phys. Chem. A 2022, 126, 879–888. [Google Scholar] [CrossRef] [PubMed]
- Leyva, E.; Loredo-Carrillo, S.E.; Aguilar, J. Various techniques for the synthesis of 2-Nitrophenylamino-1,4-naphthoquinone derivatives. Reactions 2023, 4, 432–447. [Google Scholar] [CrossRef]
- Zhang, J.; Peng, J.; Hu, D.; Lan, Z. Investigation of nonadiabatic dynamics in the photolysis of methyl nitrate (CH3ONO2) by on-the-fly surface hopping simulation. Phys. Chem. Chem. Phys. 2021, 23, 25597–25611. [Google Scholar] [CrossRef] [PubMed]
- McKee, M.L. MCSCF study of the rearrangement of nitromethane to methyl nitrite. J. Phys. Chem. 1989, 93, 7365–7369. [Google Scholar] [CrossRef]
- Saxon, R.P.; Yuoshimi, M. Theoretical study of nitro-nitrite rearrangement of CH3NO2. Can. J. Chem. 1992, 70, 572–579. [Google Scholar] [CrossRef]
- Chang, P.; Zhou, P.; Liu, J.; Yin, S. Theoretical study on autocatalytic reaction in thermal decomposition of nitromethane. Chem. Phys. Lett. 2022, 792, 139413. [Google Scholar] [CrossRef]
- Homayoon, Z.; Bowman, J.M. Quasiclassical trajectory study of CH3NO2 decomposition via roaming mediated isomerization using a global potential energy surface. J. Phys. Chem. A 2013, 117, 11665–11672. [Google Scholar] [CrossRef]
- Zhu, R.S.; Raghunath, P.; Lin, M.C. Effect of roaming transition states upon product branching in the thermal decomposition of CH3NO2. J. Phys. Chem. A 2013, 117, 7308–7313. [Google Scholar] [CrossRef]
- Zhu, R.S.; Lin, M.C. CH3NO2 decomposition/isomerization mechanism and product branching ratios: An ab initio chemical kinetic study. Chem. Phys. Lett. 2009, 478, 11–16. [Google Scholar] [CrossRef]
- Isegawa, M.; Liu, F.; Maeda, S.; Morokuma, K. Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths. J. Chem. Phys. 2014, 140, 244310. [Google Scholar] [CrossRef]
- Arenas, J.F.; Otero, J.C.; Peláez, D.; Soto, J. Role of surface crossings in the photochemistry of nitromethane. J. Chem. Phys. 2005, 122, 084324. [Google Scholar] [CrossRef] [PubMed]
- Arenas, J.F.; Otero, J.C.; Peláez, D.; Soto, J. The ground and excited state potential energy surfaces of nitromethane related to its dissociation dynamics after excitation at 193 nm. J. Chem. Phys. 2003, 119, 7814–7823. [Google Scholar] [CrossRef]
- Sumida, M.; Kohge, Y.; Yamasaki, K.; Kohguchia, H. Multiple product pathways in photodissociation of nitromethane at 213 nm. J. Chem. Phys. 2016, 144, 064304. [Google Scholar] [CrossRef] [PubMed]
- Li, W.-G.; Liu, Q.-J.; Liu, F.-S.; Liu, Z.-T. Atomic mean square displacement study of the bond breaking mechanism of energetic materials before explosive initiation. Phys. Chem. Chem. Phys. 2023, 25, 5613–5618. [Google Scholar] [CrossRef]
- Zheng, W.; Liu, Q.-J.; Liu, F.-S.; Liu, Z.-T. Triggering the mechanism of the initial reaction of energetic materials under pressure based on Raman intensity analysis. Phys. Chem. Chem. Phys. 2023, 25, 5685–5693. [Google Scholar] [CrossRef]
- Rice, B.M.; Sahu, S.; Owens, F.J. Density functional calculations of bond dissociation energies for NO2 scission in some nitroaromatic molecules. J. Mol. Struct. (THEOCHEM) 2002, 583, 69–72. [Google Scholar] [CrossRef]
- Ford, J.; Seritan, S.; Zhu, X.; Sakano, M.N.; Islam, M.M.; Strachan, A.; Martínez, T.J. Nitromethane decomposition via automated reaction discovery and an ab initio corrected kinetic model. J. Phys. Chem. A 2021, 125, 1447–1460. [Google Scholar] [CrossRef]
- Nelson, T.; Bjorgaard, J.; Greenfield, M.; Bolme, C.; Brown, K.; McGrane, S.; Scharff, R.J.; Tretiak, S. Ultrafast photodissociation dynamics of nitromethane. J. Phys. Chem. A 2016, 120, 519–526. [Google Scholar] [CrossRef]
- Dey, A.; Fernando, R.; Abeysekera, C.; Homayoon, Z.; Bowman, J.M.; Suits, A.G. Photodissociation dynamics of nitromethane and methyl nitrite by infrared multiphoton dissociation imaging with quasiclassical trajectory calculations: Signatures of the roaming pathway. J. Chem. Phys. 2014, 140, 054305. [Google Scholar] [CrossRef]
- Annesley, C.J.; Randazzo, J.B.; Klippenstein, S.J.; Harding, L.B.; Jasper, A.W.; Georgievskii, Y.; Ruscic, B.; Tranter, R.S. Thermal dissociation and roaming isomerization of nitromethane: Experiment and theory. J. Phys. Chem. A 2015, 119, 7872–7893. [Google Scholar] [CrossRef]
- Wodtke, A.M.; Hintsa, E.J.; Lee, Y.T. Infrared Multiphoton Dissociation of Three Nitroalkanes. J. Phys. Chem. 1986, 90, 3549–3558. [Google Scholar] [CrossRef]
- Bhattacharya, A.; Guo, Y.Q.; Bernstein, E.R. A comparison of the decomposition of electronically excited nitro-containing molecules with energetic moieties C-NO2, N-NO2, and O-NO2. J. Chem. Phys. 2012, 136, 024321. [Google Scholar] [CrossRef] [PubMed]
- Guo, Y.Q.; Bhattacharya, A.; Bernstein, E.R. Photodissociation dynamics of nitromethane at 226 and 271 nm at both nanosecond and femtosecond time scales. J. Phys. Chem. A 2009, 113, 85–96. [Google Scholar] [CrossRef] [PubMed]
- Matsugi, A.; Shiina, H. Thermal decomposition of nitromethane and reaction between CH3 and NO2. J. Phys. Chem. A 2017, 121, 4218–4224. [Google Scholar] [CrossRef]
- Townsend, D.; Lahankar, S.A.; Lee, S.K.; Chambreau, S.D.; Suits, A.G.; Zhang, X.; Rheinecker, J.; Harding, L.B.; Bowman, J.M. The roaming atom: Straying from the reaction path in formaldehyde decomposition. Science 2004, 306, 1158–1161. [Google Scholar] [CrossRef]
- Herath, N.; Suits, A.G. Roaming radical reactions. J. Phys. Chem. Lett. 2011, 2, 642–647. [Google Scholar] [CrossRef]
- Suits, A.G. Roaming reactions and dynamics in the van der Waals region. Annu. Rev. Phys. Chem. 2020, 71, 77–100. [Google Scholar] [CrossRef]
- Lopez, J.G.; Vayner, G.; Lourderaj, U.; Addepalli, S.V.; Kato, S.; Dejong, W.A.; Windus, T.L.; Hase, W.L. A direct dynamics trajectory study of F−+CH3OOH reactive collisions reveals a major non-IRC reaction path. J. Am. Chem. Soc. 2007, 129, 9976–9985. [Google Scholar] [CrossRef]
- Pomerantz, A.E.; Camden, J.P.; Chiou, A.S.; Ausfelder, F.; Chawla, N.; Hase, W.L.; Zare, R.N. Reaction products with internal energy beyond the kinematic limit result from trajectories far from the minimum energy path: An example from H + HBr → H2 + Br. J. Am. Chem. Soc. 2005, 127, 16368–16369. [Google Scholar] [CrossRef]
- Lourderaj, U.; Park, K.; Hase, W.L. Classical trajectory simulations of post-transition state dynamics. Int. Rev. Phys. Chem. 2008, 27, 361–403. [Google Scholar] [CrossRef]
- Suits, A.G. Roaming atoms and radicals: A new mechanism in molecular dissociation. Acc. Chem. Res. 2008, 41, 873–881. [Google Scholar] [CrossRef] [PubMed]
- Bowman, J.M.; Shepler, B.C. Roaming radicals. Annu. Rev. Phys. Chem. 2011, 62, 531–553. [Google Scholar] [CrossRef] [PubMed]
- Bowman, J.M.; Houston, P.L. Theories and simulations of roaming. Chem. Soc. Rev. 2017, 46, 7615–7624. [Google Scholar] [CrossRef] [PubMed]
- Houston, P.L.; Kable, S.H. Photodissociation of acetaldehyde as a second example of the roaming mechanism. Proc. Natl. Acad. Sci. USA 2006, 103, 16079–16082. [Google Scholar] [CrossRef]
- Harding, L.B.; Klippenstein, S.J.; Jasper, A.W. Ab initio methods for reactive potential surfaces. Phys. Chem. Chem. Phys. 2007, 9, 4055–4070. [Google Scholar] [CrossRef]
- Heazlewood, B.R.; Jordan, M.J.T.; Kable, S.H.; Selby, T.M.; Osborn, D.L.; Shepler, B.C.; Braams, B.J.; Bowman, J.M. Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. Proc. Natl. Acad. Sci. USA 2008, 105, 12719–12724. [Google Scholar] [CrossRef]
- Roos, B.O. The Complete Active Space Self-Consistent Field Method and Its Applications in Electronic Structure Calculations. In Advances in Chemical Physics; Ab initio Methods in Quantum Chemistry II; Lawley, K.P., Ed.; John Wiley & Sons: Chichester, UK, 1987; Chapter 69; p. 399. [Google Scholar]
- Roos, B.O.; Taylor, P.R.; Siegbahn, P.E.M. A complete active space SCF method (CASSCF) using a density matrix formulated super-CI approach. Chem. Phys. 1980, 48, 157–173. [Google Scholar] [CrossRef]
- Roos, B.O. The complete active space scf method in a Fock-matrix-based super-CI formulation. Int. J. Quantum Chem. 1980, 18, 175–189. [Google Scholar] [CrossRef]
- Siegbahn, P.E.M.; Almlo, J.; Heiberg, A.; Roos, B.O. The complete active space scf (CASSCF) method in a Newton-Raphson formulation with application to the HNO molecule. J. Chem. Phys. 1981, 74, 2384–2396. [Google Scholar] [CrossRef]
- Werner, H.-J.; Meyer, W. A quadratically convergent multiconfiguration-self-consistent field method with simultaneous-optimization of orbitals and cl coefficients. J. Chem. Phys. 1980, 73, 2342–2356. [Google Scholar] [CrossRef]
- Werner, H.-J.; Meyer, W. A quadratically convergent MCSCF method for the simultaneous-optimization of several states. J. Chem. Phys. 1981, 74, 5794–5801. [Google Scholar] [CrossRef]
- Olsen, J. The CASSCF method: A perspective and commentary. Int. J. Quantum. Chem. 2011, 111, 3267–3272. [Google Scholar] [CrossRef]
- Roos, B.O.; Andersson, K.; Fu, M.P.; Malmqvist, P.Â.; Serrano-Andre, L.; Pierloot, K.; Mercha, M. Multiconfigurational perturbation theory: Applications in electronic spectroscopy. Adv. Chem. Phys. 1996, 93, 219–331. [Google Scholar]
- Finley, J.; Malmqvist, P.-Å.; Roos, B.O.; Serrano-Andrés, L. The multi-state CASPT2 method. Chem. Phys. Lett. 1998, 288, 299–306. [Google Scholar] [CrossRef]
- Veryazov, V.; Widmark, P.O.; Serrano-Andrés, L.; Lindh, R.; Roos, B.O. 2MOLCAS as a development platform for quantum chemistry software. Int. J. Quantum Chem. 2004, 100, 626–635. [Google Scholar] [CrossRef]
- Aquilante, F.; Autschbach, J.; Carlson, R.K.; Chibotaru, L.F.; Delcey, M.G.; De Vico, L.; Fdez. Galván, I.; Ferré, N.; Frutos, L.M.; Gagliardi, L. Molcas 8: New capabilities for multiconfigurational quantum chemical calculations across the periodic table. J. Comp. Chem. 2016, 37, 506–541. [Google Scholar] [CrossRef]
- Fdez Galván, I.; Vacher, M.; Alavi, A.; Angeli, C.; Aquilante, F.; Autschbach, J.; Bao, J.J.; Bokarev, S.I.; Bogdanov, N.A.; Carlson, R.K.; et al. OpenMolcas: From Source Code to Insight. J. Chem. Theory Comput. 2019, 15, 5925–5964. [Google Scholar] [CrossRef]
- Aquilante, F.; Autschbach, J.; Baiardi, A.; Battaglia, S.; Borin, V.A.; Chibotaru, L.F.; Conti, I.; De Vico, L.; Delcey, M.; Ferré, N.; et al. Modern quantum chemistry with [Open] Molcas. J. Chem. Phys. 2020, 152, 214117. [Google Scholar] [CrossRef]
- Roos, B.O.; Lindh, R.; Malmqvist, P.-Å.; Veryazov, V.; Widmark, P.-O. Main group atoms and dimers studied with a new relativistic ANO basis set. J. Phys. Chem. A 2004, 108, 2851–2858. [Google Scholar] [CrossRef]
- Roos, B.O.; Lindh, R.; Malmqvist, P.-Å.; Veryazov, V.; Widmark, P.-O. New relativistic ANO basis sets for transition metal atoms. J. Phys. Chem. A 2005, 109, 6575–6579. [Google Scholar] [CrossRef]
- Møller, C.; Plesset, M.S. Note on an approximation treatment for many-electron systems. Phys. Rev. 1934, 46, 618–622. [Google Scholar] [CrossRef]
- Zhao, Y.; Truhlar, D.G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: Two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215–241. [Google Scholar]
- Frisch, M.E.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.; Cheeseman, J.R.; Scalmani, G.; Barone, V.P.G.A.; Petersson, G.A.; Nakatsuji, H.J.R.A.; et al. Gaussian 16, Revision C.02; Gaussian, Inc.: Wallingford, CT, USA, 2016. [Google Scholar]
- Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297–3305. [Google Scholar] [CrossRef]
- Weigend, F. Accurate Coulomb-fitting basis sets for H to Rn. Phys. Chem. Chem. Phys. 2006, 8, 1057–1065. [Google Scholar] [CrossRef]
- Soto, J.; Algarra, M. Electronic structure of nitrobenzene: A benchmark example of the accuracy of the multi-state CASPT2 theory. J. Phys. Chem. A 2021, 125, 9431–9437. [Google Scholar] [CrossRef] [PubMed]
- Arenas, J.F.; Otero, J.C.; Peláez, D.; Soto, J.; Serrano-Andrés, L. Multiconfigurational second-order perturbation study of the decomposition of the radical anion of nitromethane. J. Chem. Phys. 2004, 121, 4127–4132. [Google Scholar] [CrossRef]
- Arenas, J.F.; Otero, J.C.; Peláez, D.; Soto, J. Photodissociation mechanism of nitramide: A CAS-SCF and MS-CASPT2 study. J. Phys. Chem. A 2005, 109, 7172–7180. [Google Scholar] [CrossRef]
- Soto, J.; Peláez, D.; Otero, J.C.; Avila, F.J.; Arenas, J.F. Photodissociation mechanism of methyl nitrate. A study with the multistate second-order multiconfigurational perturbation theory. Phys. Chem. Chem. Phys. 2009, 11, 2631–2639. [Google Scholar] [CrossRef]
- Zhang, J.J.; Peng, J.W.; Zhu, Y.F.; Hu, D.P.; Lan, Z.G. Influence of mode-specific excitation on the nonadiabatic dynamics of methyl nitrate (CH3ONO2). J. Phys. Chem. Lett. 2023, 14, 6542–6549. [Google Scholar] [CrossRef]
- Zhang, J.J.; Peng, J.W.; Hu, D.P.; Xu, C.; Lan, Z.G. Understanding photolysis of CH3ONO2 with on-the-fly nonadiabatic dynamics simulation at the ADC(2) Level. Chin. J. Chem. Phys. 2022, 35, 451–460. [Google Scholar] [CrossRef]
- Verlet, L. Computer experiments on classical fluids. I. Thermodynamical properties of Lennard-Jones molecules. Phys. Rev. 1967, 159, 98–103. [Google Scholar] [CrossRef]
- Swope, W.C.; Andersen, H.C.; Berens, P.H.; Wilson, K.R. A computer-simulation method for the calculation of equilibrium-constants for the formation of physical clusters of molecules-application to small water clusters. J. Chem. Phys. 1982, 76, 637–649. [Google Scholar] [CrossRef]
- Schaftenaar, G.; Noordik, J.H. Molden: A pre- and post-processing program for molecular and electronic structures. J. Comput. Aided Mol. Des. 2000, 14, 123–134. [Google Scholar] [CrossRef] [PubMed]
- Allouche, A.R. Gabedit-a graphical user interface for computational chemistry softwares. J. Comput. Chem. 2011, 32, 174–182. [Google Scholar] [CrossRef]
- BBode, M.; Gordon, M.S. MacMolPlt: A graphical user interface for GAMESS. J. Mol. Graphics Modell. 1998, 16, 133–138. [Google Scholar] [CrossRef]
- Soto, J.; Peláez, D.; Algarra, M. CASPT2 study of the electronic structure and photochemistry of protonated N-nitrosodimethylamine (NDMA-H+) at 453 nm. J. Chem. Phys. 2023, 158, 204301. [Google Scholar] [CrossRef]
- Aranda, D.; Avila, F.J.; López-Tocón, I.; Arenas, J.F.; Otero, J.C.; Soto, J. An MS-CASPT2 study of the photodecomposition of 4-methoxyphenyl azide: Role of internal conversion and intersystem crossing. Phys. Chem. Chem. Phys. 2018, 20, 7764–7771. [Google Scholar] [CrossRef]
- Soto, J.; Otero, J.C.; Avila, F.J.; Peláez, D. Conical intersections and intersystem crossings explain product formation in photochemical reactions of aryl azides. Phys. Chem. Chem. Phys. 2019, 21, 2389–2396. [Google Scholar] [CrossRef]
- Soto, J. Photochemistry of 1-phenyl-1-diazopropane and its Diazirine isomer: A CASSCF and MS-CASPT2 study. J. Phys. Chem. A 2022, 126, 8372–8379. [Google Scholar] [CrossRef]
- Peláez, D.; Arenas, J.F.; Otero, J.C.; Soto, J. A complete active space self-consistent field study of the photochemistry of nitrosamine. J. Chem. Phys. 2006, 125, 164311. [Google Scholar] [CrossRef]
- Soto, J.; Arenas, J.F.; Otero, J.C.; Peláez, D. Effect of an S1/S0 conical intersection on the chemistry of nitramide in its ground state. A comparative CASPT2 study of the nitro-nitrite isomerization reactions in nitramide and nitromethane. J. Phys. Chem. A 2006, 110, 8221–8226. [Google Scholar] [CrossRef] [PubMed]
- Arenas, J.F.; Centeno, S.P.; López-Tocón, I.; Peláez, D.; Soto, J. DFT and CASPT2 study of two thermal reactions of nitromethane: C-N bond cleavage and nitro-to-nitrite isomerization. An example of the inverse symmetry breaking deficiency in density functional calculations of an homolytic dissociation. J. Mol. Struct. (THEOCHEM) 2003, 630, 17–23. [Google Scholar] [CrossRef]
- Ruscic, B.; Pinzon, R.E.; Morton, M.L.; von Laszevski, G.; Bittner, S.J.; Nijsure, S.G.; Amin, K.A.; Minkoff, M.; Wagner, A.F. Introduction to active thermochemical tables: Several “key” enthalpies of formation revisited. J. Phys. Chem. A 2004, 108, 9979–9997. [Google Scholar] [CrossRef]
- Ruscic, B.; Pinzon, R.E.; von Laszewski, G.; Kodeboyina, D.; Burcat, A.; Leahy, D.; Montoy, D.; Wagner, A.F. Active Thermochemical Tables: Thermochemistry for the 21st century. J. Phys. Conf. Ser. 2005, 16, 561–570. [Google Scholar] [CrossRef]
- Ruscic, B.; Bross, D.H. Active Thermochemical Tables (ATcT), Values Based on Ver. 1.124 of the Thermochemical Network. 2022. Available online: https://atct.anl.gov/Thermochemical%20Data/version%201.124/index.php (accessed on 7 March 2025).
- Cox, A.P.; Waring, S. Microwave-spectrum and structure of nitromethane. J. Chem. Soc. Faraday Trans. II 1972, 68, 1060–1071. [Google Scholar] [CrossRef]
- Turner, P.H.; Corkill, M.J.; Cox, A.P. Microwave-spectra and structures of cis-methyl nitrite and trans-methyl nitrite-methyl barrier in trans-methyl nitrite. J. Phys. Chem. 1979, 83, 1473–1482. [Google Scholar] [CrossRef]
- Van der Veken, B.J.; Maas, R.; Guirgis, G.A.; Stidham, G.A.; Sheehan, T.G.; Durig, J.R. Infrared spectrum, ab initio calculations, barriers to internal-rotation, and structural parameters for methyl nitrite. J. Phys. Chem. 1990, 94, 4029–4039. [Google Scholar] [CrossRef]
- Turner, P.H.; Cox, A.P. Dipole Moment of Acetaldehyde. Microwave-spectrum, structure, dipole-moment and centrifugal-distortion of nitrosomethane-dipole-moment of acetaldehyde. J. Chem. Soc. Faraday Trans. II 1978, 74, 533–559. [Google Scholar] [CrossRef]
- Soto, J. Identification of the photoreactive species of protonated N-nitrosopiperidine in acid medium: A CASPT2 and DFT study. J. Phys. Chem. A 2023, 127, 9781–9786. [Google Scholar] [CrossRef]
- Soto, J.; Peláez, D.; Otero, J.C. A SA-CASSCF and MS-CASPT2 study on the electronic structure of nitrosobenzene and its relation to its dissociation dynamics. J. Chem. Phys. 2021, 154, 044307. [Google Scholar] [CrossRef]
- Liu, M.K.; Li, J.; Li, Q.S.; Li, Z.S. Theoretical insights into photo-induced isomerization mechanisms of phenylsulfinyl radical PhSO˙. Phys. Chem. Chem. Phys. 2022, 24, 6266–6273. [Google Scholar] [CrossRef] [PubMed]
- Mu, D.; Li, Q.S. A theoretical study on the photochemical generation of phenylborylene from phenyldiazidoborane. Phys. Chem. Chem. Phys. 2023, 25, 8074–8081. [Google Scholar] [CrossRef] [PubMed]
- Peng, X.L.; Migani, A.; Li, Q.S.; Li, Z.S.; Blancafort, L. Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines. Phys. Chem. Chem. Phys. 2018, 20, 1181–1188. [Google Scholar] [CrossRef]
- Soto, J.; Algarra, M.; Peláez, D. Nitrene formation is the first step of the thermal and photochemical decomposition reactions of organic azides. Phys. Chem. Chem. Phys. 2022, 24, 5109–5115. [Google Scholar] [CrossRef]
- Arenas, J.F.; Marcos, J.I.; López-Tocón, I.; Otero, J.C.; Soto, J. Potential-energy surfaces related to the thermal decomposition of ethyl azide: The role of intersystem crossings. J. Chem. Phys. 2000, 113, 2282–2289. [Google Scholar] [CrossRef]
- Blahous, C.P., III; Yates, B.F.; Xie, Y.; Schaefer, H.F., III. Symmetry-breaking in the NO2 sigma-radical-construction of the 2A1-state and 2B2-state with Cs symmetry complete active space self-consistent-field wave-functions. J. Chem. Phys. 1990, 93, 8105–8109. [Google Scholar] [CrossRef]
Reaction | Method | ΔdG a | ΔdEe b | ΔdH c | ΔdH d |
---|---|---|---|---|---|
CH3NO2(g) → CH3(g) + NO2(g) | CASPT2 | 65.95 | |||
(0 K) | 58.76 | 58.76 | 59.16 | ||
(298.15 K) | 50.83 | 60.10 | 61.00 | ||
MP2/HF | 66.61 | ||||
(0 K) | 63.71 | 63.71 | |||
(298.15 K) | 56.70 | 65.06 | |||
M062X | 67.93 | ||||
(0 K) | 60.51 | 60.51 | |||
(298.15 K) | 53.35 | 61.93 | |||
t-CH3ONO(g) → CH3O(g)+NO(g) | CASPT2 | 46.48 | |||
(0 K) | 42.60 | 42.60 | 41.11 | ||
(298.15 K) | 33.13 | 43.99 | 42.32 | ||
MP2/HF | 51.10 | ||||
(0 K) | 49.28 | 49.28 | |||
(298.15 K) | 39.79 | 50.69 | |||
M062X | 42.63 | ||||
(0 K) | 37.86 | 37.86 | |||
(298.15 K) | 28.31 | 39.40 | |||
CH3NO2(g) → CH3NO(g)+O(3P)(g) | CASPT2 | 99.53 | |||
(0 K) | 95.32 | 95.32 | 92.83 | ||
(298.15 K) | 88.19 | 96.47 | 94.35 | ||
MP2/HF | 104.88 | ||||
(0 K) | 100.44 | 100.44 | |||
(298.15 K) | 93.46 | 101.57 | |||
M062X | 96.82 | ||||
(0 K) | 92.53 | 92.53 | |||
(298.15 K) | 85.47 | 93.68 |
Reaction | ΔaG a | ΔaEe b | ΔaH c | ΔrH d | ΔrH d | |
---|---|---|---|---|---|---|
CH3NO2(g) t-CH3ONO(g) | CASPT2 | 69.25 | ||||
(0 K) | 66.31 | 66.31 | 2.55 | 1.99 | ||
(298.15 K) | 66.66 | 66.42 | 2.66 | 2.45 | ||
MP2 | 71.84 | |||||
(0 K) | 69.19 | 69.19 | 6.10 | |||
(298.15 K) | 69.91 | 69.12 | 5.91 | |||
M062X | 73.15 | |||||
(0 K) | 70.77 | 70.77 | 2.10 | |||
(298.15 K) | 71.33 | 70.77 | 2.44 | |||
CH3NO2(g) CH2N(O)OH(g) | CASPT2 | 66.54 | ||||
(0 K) | 63.01 | 63.01 | 12.88 | |||
(298.15 K) | 64.98 | 62.54 | 12.76 | |||
MP2 | 66.35 | |||||
(0 K) | 62.86 | 62.86 | 16.32 | |||
(298.15 K) | 62.86 | 62.95 | 16.20 | |||
M062X | 65.66 | |||||
(0 K) | 62.19 | 62.19 | 12.52 | |||
(298.15 K) | 63.25 | 61.77 | 12.33 | |||
t-CH3ONO(g) CH2O(g) + HNO(g) | CASPT2 | 43.80 | ||||
(0 K) | 38.76 | 38.76 | 14.34 | 13.62 | ||
14.85 | ||||||
(298.15 K) | 38.90 | 38.68 | 15.97 | |||
MP2 | 41.94 | |||||
(0 K) | 37.69 | 37.69 | 13.42 | |||
(298.15 K) | 37.27 | 37.99 | 15.06 | |||
M062X | 49.92 | |||||
(0 K) | 45.88 | 45.88 | 14.92 | |||
(298.15 K) | 46.73 | 45.54 | 16.06 | |||
t-CH3ONO(g) c-CH3ONO(g) | CASPT2 | 12.12 | ||||
(0 K) | 11.62 | 11.62 | −0.86 | −0.74 | ||
(298.15 K) | 11.47 | 12.28 | −0.60 | −0.70 | ||
MP2 | 11.26 | |||||
(0 K) | 10.63 | 10.63 | −1.11 | |||
(298.15 K) | 10.42 | 10.75 | −0.94 | |||
M062X | 10.95 | |||||
(0 K) | 10.48 | 10.48 | −1.29 | |||
(298.15 K) | 11.46 | 9.99 | −1.66 |
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Soto, J. CASPT2 Study of the Unimolecular Reactions of Nitromethane—A Look at the Roaming Reactions in the Decomposition of Nitromethane: An Exergonic Route at High Temperatures. Reactions 2025, 6, 21. https://doi.org/10.3390/reactions6010021
Soto J. CASPT2 Study of the Unimolecular Reactions of Nitromethane—A Look at the Roaming Reactions in the Decomposition of Nitromethane: An Exergonic Route at High Temperatures. Reactions. 2025; 6(1):21. https://doi.org/10.3390/reactions6010021
Chicago/Turabian StyleSoto, Juan. 2025. "CASPT2 Study of the Unimolecular Reactions of Nitromethane—A Look at the Roaming Reactions in the Decomposition of Nitromethane: An Exergonic Route at High Temperatures" Reactions 6, no. 1: 21. https://doi.org/10.3390/reactions6010021
APA StyleSoto, J. (2025). CASPT2 Study of the Unimolecular Reactions of Nitromethane—A Look at the Roaming Reactions in the Decomposition of Nitromethane: An Exergonic Route at High Temperatures. Reactions, 6(1), 21. https://doi.org/10.3390/reactions6010021