The case of the weak N-X bond:: Ab initio, semi-experimental, and experimental equilibrium structures of XNO (X = H, F, Cl, OH) and FNO2
The case of the weak N-X bond:: Ab initio, semi-experimental, and experimental equilibrium structures of XNO (X = H, F, Cl, OH) and FNO2
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DOI：
10.1021/jp064769v
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发表时间：
2006-12-21
影响因子：
2.9
通讯作者：
Dehayem-Kamadjeu, Alix
中科院分区：
文献类型：
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作者：
Demaison, Jean;Csaszar, Attila G.;Dehayem-Kamadjeu, Alix
FNO、ClNO、HONO和FNO2的平衡结构已经用三种不同的、有些互补的方法确定：完全实验、半实验(平衡转动常数由实验的有效基态转动常数和从头算立方力场导出)和从头算，其中几何优化通常是在非相对论电子结构理论的耦合团簇水平上使用小到非常大的高斯基组进行的。为了便于比较，还重新确定了HNO和N2O的平衡结构，证实和推广了以前的结果。对于所研究的每个化合物，半实验方法给出的结构参数与可靠的实验结果符合得很好。由于对电子相关性的处理不充分，单参考CCSD(T)方法给出的N-X(X=F，Cl，OH)键太强，而缔合键长明显太短。这种差异随着基组大小的增加而增大。在CCSDTQ水平上对电子相关的更详细的处理解决了这个问题，并导致了键长的增加，正确地反映了这些XNO和XNO2物种中N-X键的弱点。所确定的平衡结构的精度优于0.001埃和0.1度。
The equilibrium structures of FNO, ClNO, HONO, and FNO2 have been determined using three different, somewhat complementary methods: a completely experimental, a semi-experimental (where the equilibrium rotational constants are derived from the experimental effective ground-state rotational constants and an ab initio cubic force field), and an ab initio, where geometry optimizations are usually performed at the coupled cluster level of nonrelativistic electronic structure theory using small to very large Gaussian basis sets. For the sake of comparison, the equilibrium structures of HNO and N2O have also been redetermined, confirming and extending earlier results. The semi-experimental method gives structural parameters in good agreement with the reliable experimental results for each compound investigated. Because of inadequate treatment of electron correlation, the single-reference CCSD(T) method gives N-X (X=F, Cl, OH) bonds that are too strong and associate bond lengths that are significantly too short. The discrepancy increases with increase in the size of the basis set. A much more elaborate treatment of electron correlation at the CCSDTQ level solves this problem and results in increased bond lengths, correctly representing the weakness of the N-X bond in these XNO and XNO2 species. The equilibrium structures determined are accurate to better than 0.001 angstrom and 0.1 degrees.