CCL:G: Transition state for recombination of dibromomercury

 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 <mailto:hovell###cetem.gov.br>
 ------_=_NextPart_001_01C6393D.C86E54E0
 Content-Type: text/html;
 	charset="iso-8859-1"
 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
 <HTML><HEAD> <META HTTP-EQUIV="Content-Type"
 CONTENT="text/html; charset=iso-8859-1">
 <META content="MSHTML 6.00.2800.1528"
 name=GENERATOR></HEAD> <BODY> <DIV><FONT face=Arial
 size=2><SPAN class=718415311-24022006>Dear
 CCLers,</SPAN></FONT></DIV> <DIV><FONT face=Arial
 size=2><SPAN class=718415311-24022006>I am assuming a linear transition
 state for the recombination of a bromine radical with the bromomercury radical
 forming the dibromo molecule.</SPAN></FONT></DIV>
 <DIV><FONT face=Arial size=2><SPAN
 class=718415311-24022006>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.</SPAN></FONT></DIV> <DIV><FONT face=Arial
 size=2><SPAN class=718415311-24022006>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.</SPAN></FONT></DIV> <DIV><FONT face=Arial
 size=2><SPAN
 class=718415311-24022006></SPAN></FONT>&nbsp;</DIV>
 <DIV><FONT face=Arial size=2><SPAN class=718415311-24022006>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?</SPAN></FONT></DIV> <DIV><FONT
 face=Arial size=2><SPAN class=718415311-24022006>All ideas would be
 welcome and a summary will be posted if this post generates
 interest.</SPAN></FONT></DIV> <DIV><FONT face=Arial
 size=2><SPAN
 class=718415311-24022006>TIA</SPAN></FONT></DIV>
 <DIV><FONT face=Arial size=2><SPAN
 class=718415311-24022006>Ian</SPAN></FONT></DIV>
 <DIV><FONT face=Arial size=2><SPAN
 class=718415311-24022006></SPAN></FONT>&nbsp;</DIV>
 <DIV><FONT face=Arial size=2><SPAN
 class=718415311-24022006></SPAN></FONT>&nbsp;</DIV>
 <DIV><FONT face=Arial size=2>Ian Hovell - Ph.D. <BR>NUCLEO DE
 MODELAGEM MOLECULAR-NMM <BR>Centro de Tecnologia Mineral - CETEM
 <BR>Ministerio da Cincia e da Tecnologia- MCT <BR>Avenida Ip, No 900
 - Cidade Universitaria <BR>Ilha do Fundo Rio de Janeiro RJ Brasil
 <BR>CEP 21941-590 <BR>tel 00 55 (xx) 3865 7344 ou
 3865 - 7216 <BR>Fax 00 55 (xx) 22602837 ou 2290-4286 <BR>e-mail
 <A href="mailto:hovell###cetem.gov.br";>hovell###cetem.gov.br</A>
 <BR></FONT></DIV>
 <DIV>&nbsp;</DIV></BODY></HTML>
 ------_=_NextPart_001_01C6393D.C86E54E0--