I have attached the frequency (molecule-09-psi-f.inp.dat) output file, which also contains the list of obtained frequencies, and the optimized geometry (molecule-09-psi.inp.log.txt) in xyz format.
I'm not sure about verifying the TS-ness of a geometry, but I can predict quite accurately what geometry should be at least a single saddle point. I do this by computing torsion rotational curves. From experience, when I constrain a single torsion angle at sequential degrees, and the rest of the molecule does not undergo significant geometric changes (i.e. I generate a continuous energetic rotational curve), then the resulting local maxima a always a transition state if I perform a full relaxed transition state optimization. The attached data is coming from a TS optimization using gau_tight; however, I have also reproduced these results using gau_verytight geometry.
I have attached the rotational curve that identified the TS in question. Granted the degree sampling is sparse at 30 degrees, but I also know that is good enough for molecules that have sp3 hybridization. As you can see in the curve, 0 and 120 degrees should be TS. (Just as a side note - this curve was made using Gamess instead of Psi4. I am still having problems getting Psi4 to perform these constraint optimization without giving various errors on various inputs. With some individual input file manipulations I can get Psi4 to generate these curves. However, with Gamess I will reliably obtain optimized results using my workflow, without spending time playing around with keywords.)
I will also note that I have done these types of calculations several times using Psi4, and this is the first and only time that I have encountered this issue.
Please let me know if there is anything else that I can clarify or provide (perhaps the Gamess output?).
All the bests,
Attached molecule-09-psi.inp.log.txt (819 Bytes)
molecule-09-psi-f.inp.dat (53.9 KB)