Monash University > Science > Chemistry > Biospectroscopy

We are interested in probing the spectroscopy and structure of molecules such as: Short lived species like C₃O, NCN, vinylamine etc. of astrophysical interest, planetary interest and structural interest. CFC's, HFC's, HCFC's and other molecules of atmospheric interest. Small species used as models for biological systems such as formamide. Larger H-bonded species of biological and chemical interest. We have developed a number of methods for generation of transients, typically flow pyrolysis, photolysis and IR laser powered pyrolysis (IRLPP) and these have been coupled with our Bruker HR120 FTIR system. Vibration-rotation spectra of molecules with lifetimes ranging from NCN (t ½ » 10-3 sec) through C₃O (t_½ » 1 sec), propadienone (t_½ » 10 sec) and vinylamine(t_½ » 10 min) to difluoroacetylene (t_½ » 30 min) and chlorophosphaethyne (t_½ » 30 min) have been recorded.



The experimental setup to generate NCN. For asymmetric molecules in particular, assignment of a spectral band is often complicated because just a single band can contain thousands of resolved vibration-rotation lines. Programs have been written for computer assisted assignment of the spectra of species ranging from simple linear molecules, through near symmetric tops to highly asymmetric tops. In addition to using computer aided assignment to deal with the plethora of lines an experimental alternative has been used to reduce the number of lines. We have built a system based on a supersonic jet expansion coupled to our Bruker HR120 spectrometer and have used this to cool species down to a rotational temperature of typically 20 - 60K. Schematics of our jet nozzle cooling system. Recently we have developed an enclosive flow cooling system that allows much more flexibility for varying the temperature of the gas under study

For asymmetric molecules in particular, assignment of a spectral band is often complicated because just a single band can contain thousands of resolved vibration-rotation lines. Programs have been written for computer assisted assignment of the spectra of species ranging from simple linear molecules, through near symmetric tops to highly asymmetric tops. In addition to using computer aided assignment to deal with the plethora of lines an experimental alternative has been used to reduce the number of lines. We have built a system based on a supersonic jet expansion coupled to our Bruker HR120 spectrometer and have used this to cool species down to a rotational temperature of typically 20 - 60K. Schematics of our jet nozzle cooling system. Recently we have developed an enclosive flow cooling system that allows much more flexibility for varying the temperature of the gas under study.


The advantages that collisional cooling has over jet-cooling for FTIR spectroscopy include:

• Thermal equilibrium: in the collisionally cooled sample translational, rotational, and vibrational degrees of freedom are equally cooled. In the jet, samples remain vibrationally (and ‘conformationally’) warm.
• Temperature control: the temperature is readily increased above the boiling point of the cooling gas, but may also be lowered by pumping on the coolant or by using a different gas.
• Reduced linewidths: jet expansions for FTIR applications are not skimmed, and the range of transverse velocities probed by the beam leads to no reduction of the Doppler linewidth. The linewidths of collisionally cooled samples in thermal equilibrium are reduced.
• Greater sensitivity: the absorption path of the gas is ca. two to three orders of magnitude greater than in a supersonic jet expansion.
• Lower sample quantities: the absorption efficiency relative to the quantity of sample gas is 5-6 orders of magnitude greater.