Symmetric transition state structure

From: EWING # - at - # JCVAXA.JCU.EDU
Subject: Symmetric transition state structure
Date: Sun, 12 Jul 1992 10:18 EST

Dear Colleagues:
 I have little experience in calculating transition state structures and ran
 into something I hope some of you can enlighten me on.
 One of our transition state structures is quite symmetric (D3h) but the
 symmetry of the reaction path we're considering is lower (C3v).  We can
 find a saddle point for this transition state using C3v symmetry, but when
 we try using D3h symmetry the saddle point is not found.  Rather, the
 structure falls apart into a minimum well.  The C3v saddle point structure
 is very symmetric, D3h for all intents and purposes.  Why can't we find the
 same saddle point under D3h?  We're using Gaussian 90 for this work.
 Thank you in advance for any suggestions you may have.
 Dave Ewing
 ewing # - at - # jcvaxa.jcu.edu