关注：

1） 什么情形下要考虑非谐效应

This analysis predicts veryinteresting implications upon isotopic substitution in the dihydrogen unit. Thevibrational energy levels are lowered when heavier isotopes are introduced. Asa consequence, and again due to theanharmonicity, the H–H distance was predicted theoretically to becomesignificantly shorter when heavier isotopes (deuterium or, even better,tritium) are used in the dihydrogen ligand.