From chemistry-request@www.ccl.net Mon Aug 31 11:13:36 1998 Received: from mailrelay1.cc.columbia.edu (cu41754@mailrelay1.cc.columbia.edu [128.59.35.143]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id LAA28254 Mon, 31 Aug 1998 11:13:35 -0400 (EDT) Received: from still3.chem.columbia.edu (still3.chem.columbia.edu [128.59.112.36]) by mailrelay1.cc.columbia.edu (8.8.5/8.8.5) with SMTP id LAA16090 for <@smtp.columbia.edu:chemistry@www.ccl.net>; Mon, 31 Aug 1998 11:13:34 -0400 (EDT) Received: by still3.chem.columbia.edu (950413.SGI.8.6.12/930416.SGI.AUTO) for chemistry@www.ccl.net id LAA02299; Mon, 31 Aug 1998 11:13:33 -0400 From: "Peter Shenkin" Message-Id: <9808311113.ZM2297@still3.chem.columbia.edu> Date: Mon, 31 Aug 1998 11:13:33 -0400 In-Reply-To: patrick "CCL:Frequency calculation of transition state" (Aug 28, 10:57pm) References: X-Mailer: Z-Mail (3.2.3 08feb96 MediaMail) To: chemistry@www.ccl.net Subject: Re: CCL:Frequency calculation of transition state Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii On Aug 28, 10:57pm, patrick wrote: > Subject: CCL:Frequency calculation of transition state > > > > Hi! How are you? During computation of frequency of molecules at > transition state, one of frequencies is negative. Why? Is it a rule for > identification of transition state? Is it possible if two or more > frequencies are negative when molecules are at transition state? > > Thank you for your attention. As others will no doubt tell you, this has to do with the definition of a transition-state as a saddle-point on the potential-energy surface, and to the mathematical definition of a saddle point. This goes back to Henry Eyring (at least) and his theory of the activated complex. Certainly extrema with two or more negative "frequencies" are geometrically possible; I don't know exactly what their chemical significance, if any, would be, or how many, if any, have actually been identified. I know people have thought about this and even looked into it, and perhaps some who know will respond here. -P. -- **************** "Cultured people are the scum that floats **************** *************** on the deep river of production" (Churchill) ************** *Peter Shenkin; Chemistry, Columbia U.; shenkin@columbia.edu (212)854-5143* *MacroModel WWW page: http://www.columbia.edu/cu/chemistry/mmod/mmod.html *