From chemistry-request@www.ccl.net Sun Feb 21 22:46:55 1999 Received: from sunflare.ccs.yorku.ca (fO+QnGtiO+ucCWFGSys9rXZT8fOoT9XN@sunflare.ccs.yorku.ca [130.63.236.128]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id WAA05321 Sun, 21 Feb 1999 22:46:54 -0500 (EST) Received: from ghunter (thing02.slip.yorku.ca [130.63.219.141]) by sunflare.ccs.yorku.ca (8.8.7/8.6.11) with SMTP id WAA16207; Sun, 21 Feb 1999 22:46:45 -0500 (EST) Message-ID: <005d01be5e16$dcc8ef40$e3db3f82@ghunter> From: "ghunter" To: , "Brian Williams" Subject: Re: CCL:Two-photon spectroscopy Date: Sun, 21 Feb 1999 22:52:12 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3110.1 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Dear Brian: This may not answer your specific need, but it may help you with 2-photon spectroscopy. Just 10 years ago I published a paper (co-author R.L.P.Wadlinger, "Photons and Neutrinos as Electromagnetic Solitons", Physics Essays, Vol. 2, pp.158-172, 1989) that (among other things) predicts the threshold intensity for multi-photon (minimally 2-photon) absorption to take place. The expression for the threshold intensity is: Intensity = 4 pi h c^2/lambda^4 where h=Planck's constant, c=velocity of light, lambda=photon-wavelength. At lambda=523 nanometres the Intensity=1 megawatt per cm^2, and (as shown above) it scales like 1/lambda^4. The theory behind this expression predicts that the photon is a soliton wave whose EM field is contained within a circular ellipsoid of length lambda, and cross-sectional circumference=lambda. The expression (above) arises from the condition for closest packing of these ellipsoidal solitons. That is you need to have 2 photon-solitons in the same place at the same time (and in phase of course) for the absorption of both of them to take place. In addition to the energy of both (=twice the energy of one - which is equal to the energy difference between the initial and final states), the transition absorbs 2 times h/2pi of angular momentum, so the selection rule differs from the same-energy one-photon absorption. Since the intensity at the focus of a focused laser beam is not uniform in practice, you may need to vary the focussing around the above predicted intensity to optimise the experimental yield. A number of different experimental results (some of them intensity sensitive to optimise 2-photon [rather than 3-or-more] absorption) have confirmed the validity of the above expression for the threshold intensity. Two of them are cited in our 1989 paper. Geoffrey Hunter, Department of Chemistry, York University, Toronto, Canada M3J 1P3 Business Tel: 416-736-5306 Fax: 416-736-5936 Home Tel: 905-880-5146 Fax: 905-880-1997 email: ghunter@yorku.ca -----Original Message----- From: Brian Williams To: CHEMISTRY@www.ccl.net Date: Saturday, February 20, 1999 8:47 PM Subject: CCL:Two-photon spectroscopy >Dear all- Is there anyone on the CCL list who has any experience trying to >use a computational approach to estimating what the two-photon spectra for an organic might be? I have some understanding of how to get at UV spectra using CIS methods, but I am curious to know whether this approach or the information derived from such a calcuation might be used to get a >quick/dirty estimate of two-photon spectra. I'm starting pretty much from >scratch here, so any/all advice would be helpful. Thanks. > >Brian Williams, Chemistry > >Administrivia: This message is automatically appended by the mail exploder: >CHEMISTRY@www.ccl.net: Everybody | CHEMISTRY-REQUEST@www.ccl.net: Coordinator >MAILSERV@www.ccl.net: HELP CHEMISTRY or HELP SEARCH | Gopher: www.ccl.net 73 >Anon. ftp: www.ccl.net | CHEMISTRY-SEARCH@www.ccl.net -- archive search > Web: http://www.ccl.net/chemistry.html >---