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镜花水月1993

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虫号: 5105944
注册: 2016-10-10
专业: 催化化学

[求助] 为什么旋轨耦合后单重态与三重态的禁阻会被打破

However, 3d84s2 → 3d94s1 promotion permits sd hybridization
of Ni, and this hybrid allows to form the new
bonds in the NiC2H4 complex [33,34]. While the interaction
of C2H4 and the 3F ground state of Ni results in a diabatic
repulsive potential energy surface (Fig. 3), the 3d94s1(1D)
excited state is well suited to bind to C2H4 and it provides
diabatic surfaces that are attractive. Crossing of the two diabatic
surfaces of different spin will be weakly avoided and
spin–orbit coupling will generate two newadiabatic surfaces,
shown as the bold lines in Fig. 3. On the lower adiabatic surfaces,
the electron configuration and electron spin changes
smoothly in the course of the reaction. In a first approximation,
the barrier of the reaction has been related to the s
→ d promotion energy, and the latter can be approximated
by the atomic’s excitation term  Esd [35]. Ni reacts efficiently
because  Esd amounts only to 6 kcal/mol, compared
with 67 for Mn, 34 for Fe, and 20 kcal/mol for Co, metals
which are inert at 300 K. Observation of the NiC2H4 formation
at this temperature implies an adiabatic barrier height
no larger than 5 kcal/mol, which correlates well with a calculated
10 kcal/mol barrier for the diabatic curve crossing
above ground-state reactants.The reason why atomic Sc, Ti and V – despite their large
Esd which are comparable to the excitation energies of the
inert metals Mn, Fe, and Co – react slowly with C2H4 is
due to the fact that these ‘early’ transition metals need not
change their electron spin to bind to C2H4 (Fig. 3a for Sc). As
crossing of diabatic surfaces of the same spin will be more
strongly avoided than crossing between surfaces of different
spin, for a given  Esd value one can reasonably expect smaller adiabatic barrier heights and, consequently, enhanced
reactivity.有大侠帮解释下文献中这段话怎么回事么

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