The mean vibrational amplitudes of 1,3-butadiene, acrolein, and glyoxal hav
e been calculated by explicitly including the effects of kinematic anharmon
icity, and are compared with the corresponding amplitudes with this effect
neglected. The scaled and unsealed quantum-mechanical force fields calculat
ed at the correlated MP2/631G*//MP2/6-31G* computational level were used. T
he calculated results are also compared with the available experimental dat
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