We apply chirality sensitive microwave three-wave mixing to 4-carvomenthenol, a molecule previously uncharacterized with rotational spectroscopy. We measure its rotational spectrum in the 2-8.5 GHz range and observe three molecular conformers. We describe our method in detail, from the initial step of spectral acquisition and assignment to the final step of determining absolute configuration and enantiomeric excess. Combining fitted rotational constants with dipole moment components derived from quantum chemical calculations, we identify candidate three-wave mixing cycles which were further tested using a double resonance method. Initial optimization of the three-wave mixing signal is done by varying the duration of the second excitation pulse. With known transition dipole matrix elements, absolute configuration can be directly determined from a single measurement.

High resolution rotational spectroscopy is used to map the conformational landscape and derive conformational relaxation pathways of citronellal.

Mid-infrared spectra have been measured for cubic ice (I_c) nanoparticles (3–150 nm diameter) formed by rapid collisional cooling over a wide range of temperatures (5–209 K). Spectral diagnostics, such as the ratio of surface related dangling OH to interior H-bonded OH stretch bands, reveal the manner in which particle size depends on bath gas temperature and density, and on water molecule concentration. For particles smaller than 5 nm strained intermolecular bonds on the surface and subsurface cause the predominant OH stretch peak position to be dramatically blue shifted by up to 40 cm⁻¹. In the size regime of 8–200 nm the position of the OH stretch absorption band maximum is relatively unaffected by particle size and it is possible to measure the temperature dependence of the peak location without influences from the surface or scattering. The band maximum shifts in a linear fashion from 3218 cm⁻¹ at 30 K to 3253 cm⁻¹ at 209 K, which may assist with temperature profiling of ice particles in atmospheric clouds and extraterrestrial systems. Over the same temperature range the librational mode band shifts very little, from 870 to 860 cm⁻¹. In the water stretching and bending regions discrete spectral features associated with the surface or sub-surface layers have been detected in particles as large as 80 nm.

The rotational spectrum of trans-cinnamaldehyde ((E)-3-phenyl-2-propenal, C₉H₈O) was recorded by chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2–8.5 GHz. The odourant molecule is the essential component of cinnamon oil and causes the characteristic smell. The rotational signatures of two conformers were observed: s-trans–trans- and s-cis–trans-cinnamaldehyde. The rotational spectra of s-trans–trans-cinnamaldehyde and all of its ¹³C-monosubstituted species in natural abundance were assigned and the corresponding carbon backbone structure was determined. The second conformer s-cis–trans-cinnamaldehyde is about 9 kJ mol⁻¹ higher in energy and could also be identified in the spectrum.