From owner-chemistry@ccl.net Fri Feb 24 20:05:00 2006 From: "Shobe, David dshobe(-)sud-chemieinc.com" To: CCL Subject: CCL:G: Transition state for recombination of dibromomercury Message-Id: <-31000-060224170226-10880-cKmcLDjeBa4+HagYXhcEfA,+,server.ccl.net> X-Original-From: "Shobe, David" Content-class: urn:content-classes:message Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="iso-8859-1" Date: Fri, 24 Feb 2006 23:02:07 +0100 MIME-Version: 1.0 Sent to CCL by: "Shobe, David" [dshobe,sud-chemieinc.com] Ian, Radical recombination reactions often don't have a TS, and it's not unusual to have a TS at one level of theory and no TS at another. My advice is to run a PES (potential energy scan) varying the Hg-Br distance. If the energy is a monotonic function of the bond length, then there is no transition state (according to whichever level of theory you are using). --David Shobe, Ph.D., M.L.S. Süd-Chemie, Inc. phone (502) 634-7409 fax (502) 634-7724 Don't bother flaming me: I'm behind a firewall. -----Original Message----- > From: owner-chemistry|a|ccl.net [mailto:owner-chemistry|a|ccl.net] Sent: Friday, February 24, 2006 2:44 PM To: Shobe, David Subject: CCL:G: Transition state for recombination of dibromomercury Sent to CCL by: Ian Hovell [HOVELL/./cetem.gov.br] This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. ------_=_NextPart_001_01C6393D.C86E54E0 Content-Type: text/plain; charset="iso-8859-1" Dear CCLers, I am assuming a linear transition state for the recombination of a bromine radical with the bromomercury radical forming the dibromo molecule. According to Nikolai (J Phys. Chem. A 2005, 109, 8765-8773) the two bond lengths are 2.539 and 4.567 angstroms produced a transition state calculated using CI methods. I am trying to produce, without much success, a transition state for this recombination reaction at the mpw1pw91 DFT level. In either full or partial (where only one bond is relaxed) optimisations, the radicals either join forming the dibromo molecule, and hence no imaginary frequency, or separate completly according to the starting bond lengths. I am using the built in SDD basis set and G03w. The output produces a warning that the bromine might be hypervalent but has no d functions - could this be the problem or this this level of calculation just not up to finding the transition state for this system? All ideas would be welcome and a summary will be posted if this post generates interest. TIA Ian Ian Hovell - Ph.D. NUCLEO DE MODELAGEM MOLECULAR-NMM Centro de Tecnologia Mineral - CETEM Ministerio da Cincia e da Tecnologia- MCT Avenida Ip, No 900 - Cidade Universitaria Ilha do Fundo Rio de Janeiro RJ Brasil CEP 21941-590 tel 00 55 (xx) 3865 7344 ou 3865 - 7216 Fax 00 55 (xx) 22602837 ou 2290-4286 e-mail hovell###cetem.gov.br ------_=_NextPart_001_01C6393D.C86E54E0 Content-Type: text/html; charset="iso-8859-1"

Dear CCLers,

I am assuming a linear transition state for the recombination of a bromine radical with the bromomercury radical forming the dibromo molecule.

According to Nikolai (J Phys. Chem. A 2005, 109, 8765-8773) the two bond lengths are 2.539 and 4.567 angstroms produced a transition state calculated using CI methods.

I am trying to produce, without much success, a transition state for this recombination reaction at the mpw1pw91 DFT level. In either full or partial (where only one bond is relaxed) optimisations, the radicals either join forming the dibromo molecule, and hence no imaginary frequency, or separate completly according to the starting bond lengths.

I am using the built in SDD basis set and G03w. The output produces a warning that the bromine might be hypervalent but has no d functions - could this be the problem or this this level of calculation just not up to finding the transition state for this system?

All ideas would be welcome and a summary will be posted if this post generates interest.

TIA

Ian

Ian Hovell - Ph.D.
NUCLEO DE MODELAGEM MOLECULAR-NMM
Centro de Tecnologia Mineral - CETEM
Ministerio da Cincia e da Tecnologia- MCT
Avenida Ip, No 900 - Cidade Universitaria
Ilha do Fundo Rio de Janeiro RJ Brasil
CEP 21941-590
tel 00 55 (xx) 3865 7344 ou 3865 - 7216
Fax 00 55 (xx) 22602837 ou 2290-4286
e-mail hovell###cetem.gov.br

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