Triplet vs. singlet reactivity of 3s13p1 states of magnesium on molecular hydrogen. A theoretical ab initio SCF-CI investigation

Chaquin, Patrick; Sevin, A.; Yu, Huafeng

doi:10.1021/j100259a022

Cited by 57 publications

(52 citation statements)

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“…The general area of metal atomsmall molecule chemistry has seen considerable activity by Such knowledge of the ground state surface is a necessary quantum chemists and a few references are given in ref. 6. A prerequisite to the study of the direct excited state chemistry of pioneering study of organoaluminum species is especially A~* (~s ) + CH4.…”

Section: Introductionmentioning

confidence: 99%

The reaction of aluminum atoms with methane

Yu¹,

Goddard²

1990

Can. J. Chem.

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. Can. J. Chem. 68, 633 (1990). Ab initio SCF and CISD calculations with split valence and larger basis sets have been carried out for several possible reactions of ground state ( 2~) aluminum atoms with methane. In particular, the barriers to insertion of A1 into a CH bond to give a CH3AIH intermediate and the abstraction of a hydrogen by A1 to give AIH and CH3 have been studied. At the SCF level, transition state structures have been located and verified by vibrational analyses. In addition, intrinsic reaction coordinates (IRC) have been followed from the transition state geometries down to reactants and to products. Calculated vibrational frequencies and lowest excitation energy for the CH3AlH intermediate are in good agreement with matrix isolation experimental results. As anticipated on the basis of MO natural correlation symmetry arguments, the energy barrier to the insertion reaction is high (-50 kcal rnol-' at the CI level). The energy requirement for the abstraction reaction is similar. A1 + CH4 + HAlCH3 Insertion A1 + CH4 + HA1 + CH3 Abstraction

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Section: Introductionmentioning

confidence: 99%

The reaction of aluminum atoms with methane

Yu¹,

Goddard²

1990

Can. J. Chem.

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“…The Mg(3s 1 S 0 ) þ H 2 reaction is endoergic by 27666 cm À1 . Upon excitation at 285 nm, the Mg(3s3p 1 P 1 ) þ H 2 reaction becomes exoergic by 7340 cm À1 , leading to the MgH(v,N) product [6][7][8][34][35][36][37][38][39][40][41][42][43]. The rotational state distribution shows a bimodal feature with a major large-N component and a minor low-N component.…”

Section: Gas Cell Studies By the Pump-probe Techniquementioning

confidence: 99%

Dynamical and stereodynamical studies of alkaline-earth atom–molecule reactions

Lin

Ureña

2007

International Reviews in Physical Chemistry

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Alkaline-earth atom molecule reactions have been extensively investigated since the early days of reaction dynamics. Though these reactions have many similarities to those of corresponding alkali atoms, as one would expect from their low ionization potential, there are important differences due to the presence of the two valence electrons in the alkaline-earth atom. This feature confers a distinct dynamical or stereodynamical behaviour whose basic description and analysis is the main objective of this article. The adopted approach is phenomenological based on the huge body of data revealed by modern crossed-beam and laser pump and probe techniques with no intention to be comprehensive but rather to put into context both authors' work. The paper starts with a resume´of the experimental approaches followed by a visit to full-collision studies under gas cell, beam-gas and crossed-beam arrangements. Detailed analysis and discussion is given of the M þ H 2 (M ¼ Ca, Mg) ! MH þ H reaction family whose dynamics is discussed using their Potential Energy Surfaces. In these studies care was taken to discuss the most relevant features of the molecular reaction dynamics with emphasis on the energy selectivity and on the stereodynamical (vectorial) nature of the reaction. To this end the available data are discussed in light of topological features of the underlying potential energy surface favouring either insertion or abstraction mechanisms. Particular attention is paid to the discussion of alkaline-earth atom reactions with halogen containing molecules. In these reactions the presence of two valence electrons leads to reaction channels, as chemiluminescent or chemi-ionization reactions, which are specifically associated with the transfer of the more energetic (inner harpooning) electron, whose dynamics or stereodynamics pattern differs from those of reaction channels associated to the transfer of the first, less energetic electron as, for example, in ion-pair reactions. A full section of the paper is dedicated to photo-induced intracluster reactions and, in particular, to the transition state dynamics of the prototype Ba . . . FCH 3 þ h ! BaF þ CH 3 reaction investigated in great detail by both nanosecond and femtosecond photo-ion and photo-electron pump and probe techniques. For this system the combination of these ultrahigh resolution techniques with isotopic labelling and ab initio calculations allowed the deciphering of its ultrafast reaction mechanism. Finally, the paper ends with some concluding remarks based on the observed propensity rules or general trends found in these alkaline-earth atom reactions.

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“…If a collinear approach is followed, a substantial potential barrier as high as 30-41 kcal/ mol will impede the reaction. 6,9 This is different from the collinear collision between O( 1 D) and H 2 . The latter has been found to have a relatively small barrier, such that the H-abstraction reaction may become significant when the collisional energy exceeds 2 kcal/mol.…”

Section: Introductionmentioning

confidence: 95%

“…For the case of the excited Mg(3 1 P 1 ) state, the related reaction pathways leading to the MgH(v,N) product have been thoroughly investigated. [1][2][3][4][5][6][7][8][9] The resultant rotational state distribution shows a bimodal feature with a major large N component and a minor low N component. Like the case of O( 1 D) with H 2 , the Mg(3 1 P 1 ) -H 2 reaction is dominated by an insertion process tracking along the attractive 1 B 2 ͑C 2v symmetry͒ or 1 AЈ ͑C s symmetry͒ curve.…”

Section: Introductionmentioning

confidence: 99%

“…10,11 As Mg(3 1 P 1 ) approaches toward H 2 in C 2v symmetry, the potential surfaces split into three surfaces, 1 A 1 , 1 B 1 , and 1 B 2 , of which the 1 B 2 surface crosses the ground-state surface. 1,6,9 After the colliding species go nonadiabatically through the surface crossing, the decomposition occurs on the anisotropic ground-state surface. 9 The high-N component of the bimodal rotational distribution, affected by the strong anisotropy, is formed via a collinear collision complex before dissociating.…”

Section: Introductionmentioning

confidence: 99%

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Reaction dynamics of Mg(4 1S, 3 1D2) with H2: Harpoon-type mechanism for highly excited states

Liu

Lin

Chen

2000

The Journal of Chemical Physics

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Using a pump–probe technique, the reactions of Mg(4 1S0 and 3 1D2) with H2 have been measured to yield similar rotational distributions of MgH(v=0 and 1) as that obtained for the reaction of the Mg(3 1P1) state with H2. A series of measurements is conducted to clarify that the reactions are initiated directly by these higher states, rather than occurring from the lower 3 1P1 state following radiative and collisional relaxation. The reactivity of the Mg 4 1S0 state with H2 is found to be comparable to that of the 3 1P1 state, but about three times larger than that of the 3 1D2 state. The Mg(4 1S0, 3 1D2)–H2 reactions proceed via a harpoon-type process, and are closely associated with the Mg(3 1P1)–H2 reaction coordinate through evolution of a series of surface crossings. To support our suggestion that the harpoon mechanism is involved, the cross sections of collisional deactivation by H2 for various excited states are measured. The ratios of cross sections observed for the 3 1P1, 4 1S0, and 5 1S0 state, equal to 1:2.85:4.3, are consistent with the calculated prediction of 1:2.62:4.24. The calculated cross sections are based on a simple hard sphere model with effective radii evaluated differently. Here, the effective radii for the higher states are determined from the crossing of ionic and covalent curves, while the Mg(3 1P1)–H2 radius is estimated from the nonadiabatic crossing between the reactive 1 1B2 state and the ground state. Consistency between observation and prediction confirms that the harpoon mechanism proposed in this work is plausible.

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Triplet vs. singlet reactivity of 3s13p1 states of magnesium on molecular hydrogen. A theoretical ab initio SCF-CI investigation

Cited by 57 publications

References 2 publications

The reaction of aluminum atoms with methane

The reaction of aluminum atoms with methane

Dynamical and stereodynamical studies of alkaline-earth atom–molecule reactions

Reaction dynamics of Mg(4 1S, 3 1D2) with H2: Harpoon-type mechanism for highly excited states

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