Effect of ph on uv absorbance of benzoic acid

[jethro]

i was recently reading about uv absorbance, and i understand why species such as the phenoxide ion and aniline absorb uv radiation at longer radiation and with more efficiency than their protonated counterparts.
i have spent long hours, however, trying to figure out why a benzoate ion might absorb at a shorter wavelength, and with less efficiency, than benzoic acid.
i have attached the source which suggests that this is true; there is a graph on page 5. my last resort is to say that the source is wrong but i want to make sure... can anyone help?

 

[chemisttree]

How might dimers of benzoic acid be different at high pH vs. low pH?

http://pubs.acs.org/doi/abs/10.1021/ja00503a016"

 

[jethro]

of course!

...much appreciated, thank you.