High Resolution Spectroscopy

Overview

Molecular spectrocopy utilises light to understand the structure of molecules, typically their electronic, vibrational and rotational structure. Conventional absorption methods measure the amount light is absorbed when passing through a sample, governed by the Beer-Lambert Law:

$$ \log\frac{I_0}{I} = \epsilon \ell c $$

where $I$ is the transmitted intensity, $I_0$ is the incident intensity, $\epsilon$ is the frequency-dependent absorption coefficient, $c$ is the concentration of the sample and $\ell$ is the path length.

In cases where the value of $\epsilon$ is small and it is difficult to detect a meaningful change in the transmitted light a number of strategies are available:

• observe some other light dependant process like photofragmentation where detection is more sensitive;
• increase the concentration of the sample (though depending on the species and overall pressure this can itself lead to broadening of the spectra recorded); and/or
• increase the path length.

The last of which is what we employ predominantly here. While a long path length cell is often impractical, multi-pass cells where the light is transmitted through the sample a number of times have a similar effect. Effectively folding the length of the cell over itself multiple times.

Current Scope

In these experiments we utilise bright, broadband synchrotron radiation in the far infrared to measure the absorption of molecular species in this region at high resolution (0.00096 cm^-1). The far-IR region is where species absorb via vibrational and rotational transitions, and fitting and modelling these IR spectra yields highly accurate structural information of the species present.

We currently have ongoing projects at both the Australian Synchrotron and Canadian Light Source operating in both in-person and remote working modes. This work is in close collaboration with Dr. Duncan Wild and former Wild Group member Christian Haakansson, now working at the Univerity of Oxford.

Collaborators

• Dr. Duncan Wild
• A/Prof. Evan Robertson
• Dr. Dominique Appadoo
• Dr. Brant Billinghurst

Contact

For more info, contact peter@watsonlaserlab.com.