The past decade has seen several major technology advances in electronics operating at microwave frequencies making it possible to develop a new generation of spectrometers for molecular rotational spectroscopy. High-speed digital electronics, both arbitrary waveform generators and digitizers, continue on a Moore’s Law-like development cycle that started around 1993 with device bandwidth doubling about every 36 months. These enabling technologies were the key to designing chirped-pulse Fourier transform microwave (CP-FTMW) spectrometers which offer significant sensitivity enhancements for broadband spectrum acquisition in molecular rotational spectroscopy. A special feature of the chirped-pulse spectrometer design is that it is easily implemented at low frequency (below 8 GHz) where Balle-Flygare type spectrometers with Fabry-Perot cavity designs become technologically challenging due to the mirror size requirements. The capabilities of CP-FTMW spectrometers for studies of molecular structure will be illustrated by the collaborative research effort we have been a part of to determine the structures of water clusters – a project which has identified clusters up to the pentadecamer. A second technology trend that impacts molecular rotational spectroscopy is the development of high power, solid state sources in the mm-wave/THz regions. Results from the field of mm-wave chirped-pulse Fourier transform spectroscopy will be described with an emphasis on new problems in chemical dynamics and analytical chemistry that these methods can tackle. The third (and potentially most important) technological trend is the reduction of microwave components to chip level using monolithic microwave integrated circuits (MMIC) – a technology driven by an enormous mass market in communications. Some recent advances in rotational spectrometer designs that incorporate low-cost components will be highlighted. The challenge to the high-resolution spectroscopy community – as posed by Frank De Lucia last year at the final meeting in Columbus – is what problems can we solve when real, fully capable spectrometers become essentially free to build?

The study of cold and ultracold molecules is a rapidly growing interdisciplinary research field. The application of translationally cold molecules includes ultra-high resolution spectroscopy, tests of fundamental symmetry, coherent control, and investigation of cold and ultra cold chemistry. However, producing and trapping translationally cold molecules is still challenging. Cold free radicals are of great interest in relation to interstellar chemistry. In our laboratory, we have constructed a Zeeman decelerator for the deceleration of supersonic molecular beams of free radicals. Every paramagnetic molecule has a magnetic dipole moment, and therefore manipulation of the translational motion of free radicals is possible using inhomogeneous magnetic fields. Our decelerator consists of a series of solenoid coils, which provides periodic inhomogeneous magnetic fields of up to 7 T along the molecular beam axis. Rapid modulation of the field intensity removes the kinetic energy of paramagnetic species via the Zeeman effect. With this Zeeman decelerator, we have successfully decelerated supersonic beams of free radicals such as CH₃. The temperature of molecules thus created is low enough to trap them in an anti-Helmholtz type magnetic trap. Resonance-enhanced multiphoton ionization spectroscopy is used to confirm that radicals with specific rotational states are confined in the magnetic trap for more than several hundred micro seconds. One of the advantages of the Zeeman decelerator is it can decelerate and trap the rotational ground state of any paramagnetic molecule. We will discuss details of our Zeeman molecular decelerator, and possible applications including the study of high resolution spectroscopy and cold reactive collisions of free radicals below sub Kelvin temperatures. The work is supported by CFI funds for the Canadian Centre for Research on Ultra-Cold Systems (CRUCS) at UBC.

Chiral molecules have fascinated chemists for more than 150 years. While their physical properties are to a very good approximation identical, the two enantiomers of a chiral molecule can have completely different (bio)chemical activities. For example, the right-handed enantiomer of carvone smells of spearmint while the left-handed one smells of caraway. In addition, the active components of many drugs are of one specific handedness, such as in the case of ibuprofen. However, in nature as well as in pharmaceutical applications, chiral molecules often exist in mixtures with other chiral molecules. The analysis of these complex mixtures to identify the molecular components, to determine which enantiomers are present, and to measure the enantiomeric excesses (ee) remains a challenging task for analytical chemistry, despite its importance for modern drug development. We present here a new method of differentiating enantiomers of chiral molecules in the gas phase based on broadband rotational spectroscopy ^{1, 2}. The phase of the acquired signal bares the signature of the enantiomer, as it depends upon the combined quantity, μ_a μ_b μ_c, which is of opposite sign between enantiomers. It thus also provides information on the absolute configuration of the particular enantiomer. Furthermore, the signal amplitude is proportional to the ee. A significant advantage of our technique is its inherent mixture compatibility due to the fingerprint-like character of rotational spectra. In this contribution, we will introduce the technique and present our latest results on chiral molecule spectroscopy and enantiomer differentiation.
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¹D. Patterson, M. Schnell, J.M. Doyle, Nature 497 (2013) 475-477 ²V.A. Shubert, D. Schmitz, D. Patterson, J.M. Doyle, M. Schnell, Angewandte Chemie International Edition 53 (2014) 1152-1155

We have been studying short lived reaction intermediates and complexes containing short lived species by high-resolution spectroscopic means. Laser induced fluorescence spectrosocpy with resolutions up to 0.02 cm⁻¹is used for observations of electronic transitions, and Fourier-transform microwave (FTMW) spectroscopy and FTMW-mm-wave double resonance spectroscopy are used for observations of pure rotational spectra. Both of the methods are combined with supersonic jet sytems equipped with pulse discharge nozzles to produce short lived species. Last several years, we are concentrating on observations of short lived oxygen bearing species and their complexes especially with water. Such species are considred to be important in atmospheric chemistry, since chemistry in the earth's atmosphere mainly proceeds as oxidation reactions of trace species existing in the atmosphere, where various oxygen bearing reaction intermediates are playing important roles. Detections by high-resolution spectroscopy are expected to provide valuable information on these species. Furthermore, importance of molecular complexes containing reaction intermediates with water in atmospheric chemistry has been discussed recently, where detections of such species are highly required since quite limited experimental information has been obtained so far. In the talk, results of a number of such species, either monomers or complexes, studied recently in our laboratory will be reviewed.