基于精确的晶体结构数据并设定B=0.037nm以拟合经验参数R0是通常采用的键价参数推导方法.与此相反,作者提出从分子气相电子衍射的键长设定经验参数R0,然后从晶体结构数据拟合经验参数B.以Pb(Ⅱ)—卤素键为例,PbX_2气相电子衍射Pb—X(X=F,Cl,Br,I)键长分别为0.2036,0.2447,0.2598和0.2804nm,经拟合到最佳B值分别为0.0382,0.040,0.040,0.0386nm,与普适参数B值0.037nm有一定的差距.所提出的键价参数不仅得到比较理想的键价值和计算结果,而且保留了键价参数R_0作为单价键长明确的物理意义.The values of bond valence parameters R_0 for the bonds of main group metal halides are usually obtained by systematic analysis of the crystal structure data by assuming B=0.037 nm. In this work, conversely, the values of B were proposed to be fitted with crystal structure data on assuming the values of R_0 equal to the bond lengths of rg accurately determined by gaseous electron diffraction. As an example, the new sets of R_0 /B for the Pb(Ⅱ)-X (X=F, Cl, Br, I) bonds were obtained and fitted as 0.2036/0.0382, 0.2447/0.040, 0.2598/0.040, and 0.2804/0.0386, respectively. Compared with the values of R_0=0.203, 0.253, 0.264, and 0.278 nm based on B=0.037nm for Pb(Ⅱ )-X bonds reported in the literature, these new parameters were not only accurate and reliable for bond valence calculations, but also revealed the physical meaning inherent in every R_0 as unit valence bond length
