I Love the Smell of Results in the Morning!

Things are looking up in p-(dimethyl)amino cinnamaldehyde (pDMAC) land. Over the last couple summers one of the students I’ve been working with (Diane, that’s you!) has collected enough SERS and Raman data to begin putting together a manuscript! I’ve been working on getting some more spectra over the last couple of weeks, as well as finishing up some calculations using Gaussian 03W.

One question that comes up frequently about our spectra is if we are seeing the cis or trans isomer of pDMAC. As we dug around looking for published spectra and frequencies, we (quite happily) discovered that there aren’t any! So this means that we can write up a nice paper about it. To strengthen it, and to help us assign the vibrations, we decided to do some Gaussian calculations on the optimized geometries (which tell us that trans is more stable than cis) and predict vibrational frequencies and the Raman spectrum. Below the fold are the experimental (normal Raman, solid pDMAC) and theoretical Raman spectra (isolated molecules in gas phase, wavenumbers scaled by 0.9806).

Fatal Error

Yep, that’s the message Gaussian greeted me with today. Looks like my attempt to optimize the DMAC-Ag complex geometry failed. Sort of like this. Anybody out there have any ideas for me? Please?

Lab Update – Using Pseudopotentials

I’m trying to finish up some of the work on p-dimethyl aminocinnamaldehyde (DMAC) that started several years ago. My goal is to refine the theoretical calculations that Diane performed last summer by including Ag atoms[1]. Hopefully the calculations will help us understand how DMAC adsorbs at the Ag surface, and maybe support the vibrational assignments that Diane made.

Three Day POGIL Lab Workshop June 2009

I am serving as the local host of a three day POGIL (process oriented guided inquiry learning) workshop on labs for the next three days. If you follow the link, you can learn a lot about POGIL. This is the third three day POGIL workshop that Linfield has hosted, and the fifth workshop that I’ve been part of either as a participant or participant/host.

If you really want to know a lot about POGIL, follow the link above. Briefly, POGIL is

What Do “Good” Ag Colloids Look Like?

If you are my faithful reader, then you know that much (all?) of the research that happens here relies on “good” silver colloids. Last week I posted a prep that results in good Ag sols. But what do I mean by good? Well, they have to look good.

Tiny Balls

One of my colleagues is good friends with the Chef at Bistro Maison here in town (as you can imagine from the name, a French bistro…).  They’ve become interested in using sodium alginate to make little balls, which they will then fill with flavor – like this post about “false caviar of cilantro“.  It turns out that when  sodium alginate is added to a calcium chloride solution, a gel forms.  The gel can then have food, liquids – lots of things added to it.

Turns out that you can also make SERS substrates in them, as described in this article.  The gel both stabilizes the particles, but is also the reductant (via photoreduction) for formation of Au or Ag (or Au/Ag core-shell) nanoparticles.  The authors found out that Au produced enhancements of up to 10⁴ (HeNe excitation at 633 nm).

This makes me think – SERS tagged foodstuff. In little balls. I think I now know the title of my next collaborative research proposal: “The Summer of Tiny Balls”.

Thermodynamics in Song

Over at the World’s Fair, they’ve posted a song about love and thermodynamics.  This made me wonder, are there more thermo songs out there?  A quick search turned up just one (scroll down to the Flanders and Swan section).  If anyone who reads this knows of more, please post them in the comments section.

SERS – A Unified Approach

Last wee was Thanksgiving break, and I enjoyed a week off from teaching.  One of the things I had time to do is sit down and read an article that was published in the Journal of Physical Chemistry C last March, “A Unified Approach to Surface-Enhanced Raman Spectroscopy” (Lombardi and Birke, Volume 112, pgs 5605-5617, DOI 10.1021/jp800167v).

Lombardi and Birke’s article pulls together the many different explanations for the large Raman enhancements observed for molecules adsorbed to coinage metal surfaces with atomic scale roughness features – surface-Enhanced Raman scattering (SERS).  They argue that it is important to consider all of the resonances in such systems, which include

1. Surface plasmon resonances
2. Molecular state resonances
3. Charge transfer resonances

After laying out the theoretical expressions that govern the magnitued of the polarizability tensor in these systems, they run through a series of examples that illustrate the theory.  The theory is consistent with SERS of molecules on any type of nanoparticle or electrode surface, and for any type of excitation situation (like where the laser frequency is far from molecular and charge transfer resonances, to where the laser’s frequency is resonant).  If you’re interested in learning more, read on as I summarize.  Even better, get a copy of the original article and read it!