Test in d2n
Here is a spreadsheet (gastransmission.xls) with transmission data measured at Syracuse on behalf of BTeV years ago. It shows essentially 100% transmission from 180--350nm. Unfortunately, I don't know the length of gas that was sampled, so a transmissability/absorption length can not be computed, but absorption is basically zero over this range.
Hall B measured a sample of the C4F8O we used for transversity/d2n in 2009. Their report is also attached (2008-033.pdf). The relevant figure is #22 (C4F8O). The transmittance plots are over 1.5m of gas at 1 atm. There is essentially no measured absorption from 200nm--500nm. NOTE: please do not be fooled/misled by figures 12, 14, 15, etc. The observed fall off in those plots is an artifact of the UV-glass PMT used for those data. Figure 22 has data taken after they borrowed a quartz-face PMT and you see it is basically flat up to the region where the PMT quantum efficiency starts to die (ie. 200nm for this particular tube). (See also: comment at bottom of p.6).
The Hall B data and the Syracuse data both support the conclusion that C4F8O is essentially 100% transparent down to 180nm over a nominal 1.5m of gas length.
I am not aware of measured transmittance/absorption data below for wavelengths below 180nm.