At least two reasons for the wider range of absorption
One is the interaction of one atom to others, like crystalline structure to which a single energy becoming a band of energy.
The other is related with distortion of bonds (length and angle of bonding), amorphous structure (like glass) makes the absorption band even wider because its bonds are generally distorted.
Inferred absorption is for lower energy bonds, which is used for bonding measurement in molecules. One kind of atom, in a mass of molecules, interacts with all other surrounding atoms and its bonding is expected to be distorted from location to location.

根据测不准原理，能带变宽说明寿命变短．这句话你觉得说了有用吗？sohu和serious已经说过了，看上去你不是也不信吗．