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Sanz-Novo M, Redondo P, Sánchez CI, Largo A, Barrientos C, Sordo JÁ. Structure and Spectroscopic Insights for CH 3PCO Isomers: A High-Level Quantum Chemical Study. J Phys Chem A 2024; 128:4083-4091. [PMID: 38723198 PMCID: PMC11129311 DOI: 10.1021/acs.jpca.4c01370] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2024] [Revised: 05/01/2024] [Accepted: 05/01/2024] [Indexed: 05/24/2024]
Abstract
The exploration of phosphorus-bearing species stands as a prolific field in current astrochemical research, particularly within the context of prebiotic chemistry. Herein, we have employed high-level quantum chemistry methodologies to predict the structure and spectroscopic properties of isomers composed of a methyl group and three P, C, and O atoms. We have computed relative and dissociation energies, as well as rotational, rovibrational, and torsional parameters using the B2PLYPD3 functional and the explicitly correlated coupled cluster CCSD(T)-F12b method. Based upon our study, all the isomers exhibit a bent heavy atom skeleton with CH3PCO being the most stable structure, regardless of the level theory employed. Following in energy, we found four high-energy isomers, namely, CH3OCP, CH3CPO, CH3COP, and CH3OPC. The computed adiabatic dissociation energies support the stability of all [CH3, P, C, O] isomers against fragmentation into CH3 and [P, C, O]. Torsional barrier heights associated with the methyl internal rotation for each structure have been computed to evaluate the occurrence of possible A-E splittings in the rotational spectra. For the most stable isomer, CH3PCO, we found a V3 barrier of 82 cm-1, which is slightly larger than that obtained experimentally for the N-counterpart, CH3NCO, yet still very low. Therefore, the analysis of its rotational spectrum can be anticipated as a challenging task owing to the effect of the CH3 internal rotation. The complete set of spectroscopic constants and transition frequencies reported here for the most stable isomer, CH3PCO, is intended to facilitate eventual laboratory searches.
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Affiliation(s)
- Miguel Sanz-Novo
- Centro
de Astrobiología (CAB), INTA-CSIC, Carretera de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
| | - Pilar Redondo
- Departamento
de Química Física, Universidad
de Valladolid, 47011 Valladolid, Spain
| | - Clara Isabel Sánchez
- Departamento
de Química Física, Universidad
de Valladolid, 47011 Valladolid, Spain
| | - Antonio Largo
- Departamento
de Química Física, Universidad
de Valladolid, 47011 Valladolid, Spain
| | - Carmen Barrientos
- Departamento
de Química Física, Universidad
de Valladolid, 47011 Valladolid, Spain
| | - José Ángel Sordo
- Departamento
de Química Física y Analítica, Laboratorio de
Química Computacional, Facultad de Química, Universidad de Oviedo, Julián Clavería 8, 33006 Oviedo, Principado de Asturias, Spain
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2
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Brahem S, Missaoui D, Yazidi O, Najar F, Senent ML. Theoretical structural and spectroscopic characterization of peroxyacetic acid (CH 3-CO-OOH): study of the far infrared region. Phys Chem Chem Phys 2024; 26:12600-12609. [PMID: 38597218 DOI: 10.1039/d3cp05783f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
Peroxyacetic acid, a non-rigid oxygenated organic molecule which acts in the atmosphere as a reservoir of HOX and ROX radicals, is studied using highly correlated ab initio methods with the aim of its spectroscopic characterization in the gas phase. The study focuses on the far infrared region providing reliable rovibrational parameters such as energy levels and splittings. The molecule presents three conformers that inter-convert by internal rotation, drawing a potential energy surface of 12 minima. One of them shows prominent stability due to the formation of one weak intramolecular bond between the hydrogen atom of the hydroperoxy group and the oxygen atom of the carbonyl group. For the three minimum energy structures, rotational constants and centrifugal distortion constants are provided. It may be expected that the most stable conformer is the only one contributing to the spectral features in further measurements at low temperature. In this structure, the methyl torsional barrier has been found to be very low, V3 = 88.6 cm-1 producing a splitting of 2.262 cm-1 for the ground vibrational state. The study confirms that the ν20 torsional mode interacts strongly with the other two torsional modes ν19 and ν21, but slightly with the remaining vibrations. Then, a variational procedure in three dimensions allows the exploration of the low-frequency modes. The methyl torsional fundamental ν21 was found to be 49.1 cm-1 (Ai) and 33.4 cm-1 (E). The fundamentals of ν20 (C-O bond torsion) and ν19 (OH torsion) have been computed to be 216.7 cm-1 (A2) and 218.5 cm-1 (E) and 393.6 cm-1 (A2) and 394.1 cm-1. Since non-rigidity can have effects on the reactivity due to the conformer interconversion, and transitions involving low-lying levels can be observed with many spectroscopic techniques, this work can help kinetic studies and assignments of further spectroscopic studies needed for the detection in the gas phase of trace molecules.
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Affiliation(s)
- Sinda Brahem
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunisia
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain
- Unidad Asociada GIFMAN, CSIC-UHU, Spain.
| | - Dorsaf Missaoui
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunisia
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain
- Unidad Asociada GIFMAN, CSIC-UHU, Spain.
| | - Ounaies Yazidi
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunisia
| | - Faouzi Najar
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunisia
| | - María Luisa Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain
- Unidad Asociada GIFMAN, CSIC-UHU, Spain.
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3
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Toumi I, Dalbouha S, Al-Mogren MM, Yazidi O, Jaïdane NE, Carvajal M, Senent ML. Theoretical Spectroscopic Study of Two Ketones of Atmospheric Interest: Methyl Glyoxal (CH 3COCHO) and Methyl Vinyl Ketone (CH 3COCH═CH 2). J Phys Chem A 2022; 126:7230-7241. [PMID: 36178377 PMCID: PMC9574920 DOI: 10.1021/acs.jpca.2c05653] [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] [Indexed: 11/28/2022]
Abstract
Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core-valence correlation-consistent basis sets. The work focuses on the far-infrared region. At the employed level of theory, the rotational constants can be determined to within a few megahertz of the experimental data. Both molecules present two conformers, trans/cis and antiperiplanar (Ap)/synperiplanar (Sp), respectively. trans-Methyl glyoxal and Ap-methyl vinyl ketone are the preferred structures. cis-Methyl glyoxal is a secondary minimum of very low stability, which justifies the unavailability of experimental data in this form. In methyl vinyl ketone, the two conformers are almost isoenergetic, but the interconversion implies a relatively high torsional barrier of 1798 cm-1. A very low methyl torsional barrier was estimated for trans-methyl glyoxal (V3 = 273.6 cm-1). Barriers of 429.6 and 380.7 cm-1 were computed for Ap- and Sp-methyl vinyl ketone. Vibrational second-order perturbation theory was applied to determine the rovibrational parameters. The far-infrared region was explored using a variational procedure of reduced dimensionality. For trans-methyl glyoxal, the ground vibrational state was estimated to split by 0.067 cm-1, and the two low excited energy levels (1 0) and (0 1) were found to lie at 89.588 cm-1/88.683 cm-1 (A2/E) and 124.636 cm-1/123.785 cm-1 (A2/E). For Ap- and Sp-methyl vinyl ketone, the ground vibrational state splittings were estimated to be 0.008 and 0.017 cm-1, respectively.
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Affiliation(s)
- Insaf Toumi
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisia
| | - Samira Dalbouha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V de Rabat, BP 1014 Rabat, Morocco.,Laboratoire de Chimie Organique et de Chimie Physique, Equipe de recherche: Modélisation Moléculaire, Matériaux et Environnement, Département de chimie, Faculté des Sciences d'Agadir, Université Ibn Zohr d'Agadir, BP 8106 Agadir, Morocco
| | - Muneerah Mogren Al-Mogren
- Chemistry Department, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia
| | - Ounaies Yazidi
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisia.,Institut Préparatoire aux Etudes d'Ingénieurs el Manar, Université de Tunis El Manar, BP 244, 2092 Tunis, Tunisia
| | - Nejm-Eddine Jaïdane
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisia
| | - Miguel Carvajal
- Departamento de Ciencias Integradas, Centro de Estudios Avanzados en Física, Matemática y Computación, Unidad Asociada GIFMAN, CSIC-UHU, Universidad de Huelva, 21071 Huelva, Spain.,Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
| | - María Luisa Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid, Spain.,Unidad Asociada GIFMAN, CSIC-UHU, Universidad de Huelva, 21071 Huelva, Spain
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El Hadki H, Gámez VG, Dalbouha S, Marakchi K, Kabbaj OK, Komiha N, Carvajal M, Senent Diez ML. Theoretical spectroscopic study of acetyl (CH 3CO), vinoxy (CH 2CHO), and 1-methylvinoxy (CH 3COCH 2) radicals. Barrierless formation processes of acetone in the gas phase. OPEN RESEARCH EUROPE 2022; 1:116. [PMID: 37645120 PMCID: PMC10445905 DOI: 10.12688/openreseurope.14073.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 03/10/2022] [Indexed: 08/31/2023]
Abstract
Background: Acetone is present in the earth´s atmosphere and extra-terrestrially. The knowledge of its chemical history in these environments represents a challenge with important implications for global tropospheric chemistry and astrochemistry. The results of a search for efficient barrierless pathways producing acetone from radicals in the gas phase are described in this paper. The spectroscopic properties of radicals needed for their experimental detection are provided. Methods: The reactants were acetone fragments of low stability and small species containing C, O and H atoms. Two exergonic bimolecular addition reactions involving the radicals CH 3, CH 3CO, and CH 3COCH 2, were found to be competitive according to the kinetic rates calculated at different temperatures. An extensive spectroscopic study of the radicals CH 3COCH 2 and CH 3CO, as well as the CH 2CHO isomer, was performed. Rovibrational parameters, anharmonic vibrational transitions, and excitations to the low-lying excited states are provided. For this purpose, RCCSD(T)-F12 and MRCI/CASSCF calculations were performed. In addition, since all the species presented non-rigid properties, a variational procedure of reduced dimensionality was employed to explore the far infrared region. Results: The internal rotation barriers were determined to be V 3=143.7 cm -1 (CH 3CO), V 2=3838.7 cm -1 (CH 2CHO) and V 3=161.4 cm -1 and V 2=2727.5 cm -1 (CH 3COCH 2).The splitting of the ground vibrational state due to the torsional barrier have been computed to be 2.997 cm -1, 0.0 cm -1, and 0.320 cm -1, for CH 3CO, CH 2CHO, and CH 3COCH 2, respectively. Conclusions: Two addition reactions, H+CH 3COCH 2 and CH 3+CH 3CO, could be considered barrierless formation processes of acetone after considering all the possible formation routes, starting from 58 selected reactants, which are fragments of the molecule. The spectroscopic study of the radicals involved in the formation processes present non-rigidity. The interconversion of their equilibrium geometries has important spectroscopic effects on CH 3CO and CH 3COCH 2, but is negligible for CH 2CHO.
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Affiliation(s)
- Hamza El Hadki
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Victoria Guadalupe Gámez
- Departamento de Química y Física Teóricas, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Madrid, 28006, Spain
| | - Samira Dalbouha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
- Equipe de recherche : Matériaux et Applications Environnementales, Laboratoire de Chimie Appliquée et Environnement, Département de chimie, Faculté des Sciences d’Agadir, Université Ibn Zohr, Agadir, B.P 8106, Morocco
| | - Khadija Marakchi
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Oum Keltoum Kabbaj
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Najia Komiha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Miguel Carvajal
- Departamento de Ciencias Integradas, Centro de Estudios Avanzados en Física, Matemática y Computación; Unidad Asociada GIFMAN, CSIC-UHU, Universidad de Huelva, Huelva, 21071, Spain
- Instituto Universitario Carlos I de Física Teórica y Computacional, University of Granada, Granada, Spain
| | - Maria Luisa Senent Diez
- Departamento de Química y Física Teóricas, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Madrid, 28006, Spain
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5
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Al-Mogren MM, Senent ML. Ab Initio Study of the Large Amplitude Motions of Various Monosubstituted Isotopologues of Methylamine (CH 3-NH 2). Front Chem 2021; 9:751203. [PMID: 34631671 PMCID: PMC8495219 DOI: 10.3389/fchem.2021.751203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 09/08/2021] [Indexed: 11/13/2022] Open
Abstract
CCSD(T)-F12 theory is applied to determine electronic ground state spectroscopic parameters of various isotopologues of methylamine (CH3-NH2) containing cosmological abundant elements, such as D, 13C and 15N. Special attention is given to the far infrared region. The studied isotopologues can be classified in the G12, G6 and G4 molecular symmetry groups. The rotational and centrifugal distortion constants and the anharmonic fundamentals are determined using second order perturbation theory. Fermi displacements of the vibrational bands are predicted. The low vibrational energy levels corresponding to the large amplitude motions are determine variationally using a flexible three-dimensional model depending on the NH2 bending and wagging and the CH3 torsional coordinates. The model has been defined assuming that, in the amine group, the bending and the wagging modes interact strongly. The vibrational levels split into six components corresponding to the six minima of the potential energy surface. The accuracy of the kinetic energy parameters has an important effect on the energies. Strong interactions among the large amplitude motions are observed. Isotopic effects are relevant for the deuterated species.
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Affiliation(s)
| | - María Luisa Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de La Materia, IEM-CSIC, Madrid, Spain
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6
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Large Amplitude Motions of Pyruvic Acid (CH 3-CO-COOH). Molecules 2021; 26:molecules26144269. [PMID: 34299546 PMCID: PMC8303138 DOI: 10.3390/molecules26144269] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 07/08/2021] [Accepted: 07/10/2021] [Indexed: 11/17/2022] Open
Abstract
Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the Cs point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406-986 cm-1 region and represent excitations of the ν24 (skeletal torsion) and the ν23 (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν23. The A1/E splitting of the ground vibrational state has been evaluated to be 0.024 cm-1 as it was expected given the high of the methyl torsional barrier (338 cm-1). A very good agreement with respect to previous experimental data concerning fundamental frequencies (νCAL - νEXP ~ 1 cm-1), and rotational parameters (B0CAL - B0EXP < 5 MHz), is obtained.
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7
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Boussessi R, Senent ML. Computational analysis of the far infrared spectral region of various deuterated varieties of ethylene glycol. Phys Chem Chem Phys 2020; 22:23785-23794. [PMID: 33063802 DOI: 10.1039/d0cp03315d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The far infrared spectra of three deuterated isotopologues of ethylene glycol, CH2OD-CH2OD, CH2OD-CH2OH and CH2OH-CH2OD, where the latter two species differ in their intramolecular hydrogen-bonding arrangement, are studied using highly correlated ab initio methods, vibrational second order perturbation theory and a variational procedure of reduced dimensionality. New subroutines suitable for the study of large systems with more than two interacting large amplitude motions were implemented and applied. The molecular symmetry of ethylene glycol decays by the formation of weak intramolecular bonds producing very asymmetrical stable structures. Three internal rotations contribute to the formation of a very anisotropic potential energy surface and to the puzzling distribution of the rovibrational energy levels. The ground vibrational state rotational constants and the centrifugal distortion constants (S-reduction, Ir representation) corresponding to the aGg' (G1) and gGg' (G2) forms are provided for the studied isotopologues. The low-lying vibrational levels up to 550 cm-1 are obtained variationally for J = 0. Two series of sublevels of the ground vibrational state are obtained: eight components localized in G1 lying between 0.0 and 0.3 cm-1 and eight sublevels localized in G2 lying between 138.1 and 138.4 cm-1. The gap between both sets is lower in CH2OD-CH2OD and more dispersed in the monodeuterated variety.
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Affiliation(s)
- Rahma Boussessi
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Serrano 121, Madrid 28006, Spain.
| | - María Luisa Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Serrano 121, Madrid 28006, Spain.
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8
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Dalbouha S, Senent ML. Large amplitude vibrations of acetyl isocyanate, methyl cyanoformate, and acetyl cyanate. Phys Chem Chem Phys 2019; 21:3597-3605. [DOI: 10.1039/c8cp04490b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The far infrared region of three detectable molecules sharing the empirical formula C3H3O2N, acetyl isocyanate CH3CONCO (AISO), methyl cyanoformate NC–COOCH3 (MCN) and acetyl cyanate CH3COOCN (ACN), is explored using explicitly correlated coupled cluster ab initio methods and a variational procedure designed for non-rigid species and large amplitude motions.
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Affiliation(s)
- Samira Dalbouha
- Departamento de Química y Física Teóricas
- Instituto de Estructura de la Materia, CSIC
- 28006 Madrid
- Spain
| | - María L. Senent
- Departamento de Química y Física Teóricas
- Instituto de Estructura de la Materia, CSIC
- 28006 Madrid
- Spain
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Bouallagui A, Zanchet A, Yazidi O, Jaïdane N, Bañares L, Senent ML, García-Vela A. Photodissociation of the CH 3O and CH 3S radical molecules: an ab initio electronic structure study. Phys Chem Chem Phys 2017; 19:31245-31254. [PMID: 29143005 DOI: 10.1039/c7cp06054h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic states and the spin-orbit couplings between them involved in the photodissociation process of the radical molecules CH3X, CH3X → CH3 + X (X = O, S), taking place after the Ã(2A1) ← X[combining tilde](2E) transition, have been investigated using highly correlated ab initio techniques. A two-dimensional representation of both the potential-energy surfaces (PESs) and the couplings is generated. This description includes the C-X dissociative mode and the CH3 umbrella mode. Spin-orbit effects are found to play a relevant role in the shape of the excited state potential-energy surfaces, particularly in the CH3S case where the spin-orbit couplings are more than twice more intense than in CH3O. The potential surfaces and couplings reported here for the present set of electronic states allow for the first complete description of the above photodissociation process. The different photodissociation mechanisms are analyzed and discussed in light of the results obtained.
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Affiliation(s)
- A Bouallagui
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain.
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Maté B, Molpeceres G, Timón V, Tanarro I, Escribano R, Guillemin JC, Cernicharo J, Herrero VJ. Laboratory study of methyl isocyanate ices under astrophysical conditions. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2017; 470:4222-4230. [PMID: 29861511 PMCID: PMC5975948 DOI: 10.1093/mnras/stx1461] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Methyl isocyanate has been recently detected in comet 67P/ Churyumov-Gerasimenko (67P/CG) and in the interstellar medium. New physicochemical studies on this species are now necessary as tools for subsequent studies in astrophysics. In this work, infrared spectra of solid CH3NCO have been obtained at temperatures of relevance for astronomical environments. The spectra are dominated by a strong, characteristic multiplet feature at 2350-2250 cm-1, which can be attributed to the antisymmetric stretching of the NCO group. A phase transition from amorphous to crystalline methyl isocyanate is observed at ~ 90 K. The band strengths for the absorptions of CH3NCO in ice at 20 K have been measured. Deuterated methyl isocyanate is used to help with the spectral assignment. No X-ray structure has been reported for crystalline CH3NCO. Here we advance a tentative theoretical structure, based on Density Functional Theory (DFT) calculations, derived taking as a starting point the crystal of isocyanic acid. A harmonic theoretical spectrum is calculated then for the proposed structure, and compared with the experimental data. A mixed ice of H2O and CH3NCO was formed by simultaneous deposition of water and methyl isocyanate at 20 K. The absence of new spectral features indicates that methyl isocyanate and water do not react appreciably at 20 K, but form a stable mixture. The high CH3NCO/H2O ratio reported for comet 67P/CG, and the characteristic structure of the 2350-2250 cm-1 band, make of it a very good candidate for future astronomical searches.
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Affiliation(s)
- B Maté
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
| | - G Molpeceres
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
| | - V Timón
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
| | - I Tanarro
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
| | - R Escribano
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
| | - J C Guillemin
- Institut des Sciences Chimiques de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708 Rennes Cedex 7, France
| | - J Cernicharo
- ICMM-CSIC, Molecular Astrophysics Group, c./ Sor Juana Inés de la Cruz 3, Cantoblanco, 28049, Madrid, Spain
| | - V J Herrero
- Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain
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