This question is regarding Gaussian Computational software package.
I have a system where one product forms from one conformational arrangement of molecular intermediate (conformational minimum) and another product forms from a second conformational arrangement of the same molecular intermediate (another conformational minimum). These two arrangements can be interconverted via a rotation about a single bond. In order to investigate the subsequent TS from each pathway, I also need to find the pathway that interconverts the two conformers.
How can I use Gaussian to find the rotational transition state that converts these two conformations? I have tried QST2 method using both conformers as input but did not work; I also tried doing a scan along the rotation about the single bond and do a subsequent TS search from the scan maxima but to no avail. Any other methods that I can use to find rotational transition states? I imagine the PES to be very flat, how can I improve my input for tighter convergence?