Suits Group


The Uniform-Flow Cavity Ring-Down Spectroscopy instrument is the first in the world to combine cw-CRDS with a Laval flow. With it we have recently demonstrated Simultaneous Kinetics and Ring-down (SKaR) in a Laval Flow. The instrument, designed by Nicolas Suas-David, is crrently led by Shameemah Thawoos with ongoing contributions from collaborator Dr. Gregory Hall. Suuported by NSF.

UF-CRDS (Uniform Flow–Cavity Ring Down Spectrometer) is a recently developed apparatus that couples a pulsed uniform flow with a continuous wave cavity ringdown spectrometer (cw-CRDS) [1]. This setup will complement the existing CPUF [2] microwave instrument and will facilitate the detection and characterization of reaction intermediates and related radicals produced by photolysis reactions.

The pulsed Laval flow is generated by coupling a home built piezo electric stack valve (PSV) [3] and a Laval nozzle. This unit is mounted on actuators which could be translated horizontally and vertically and placed with in a vacuum chamber. We use either 3D printed Laval nozzles designed using a matlab program developed in-house or aluminum machined nozzles. The gas is introduced to the reservoir (of about 20 cm3) by the pulsed PSV, typically at 5Hz. The gas in the reservoir expands through the Laval nozzle into the vacuum chamber producing a uniform supersonic flow.

The current apparatus can be configured either with an external cavity diode laser (ECDL), tunable between 1280-1380 nm or a distributed feedback (DFB) diode laser, tunable between 1411-1419 nm. The high sensitivity of the cw-CRDS technique itself and the tunability of the detection wavelength in the near IR range extends the ability of detection of electronic and rovibrational transitions of reactants and intermediates within low temperature Laval flow (15 to 70 K). Our main interest lies in studying reaction kinetics and spectroscopy of such species produced in uniform Laval flow, similar to what has been demonstrated by the CRESU technique using LIF [4].

Ongoing experiments focus on reaction kinetics in low temperature uniform flows, where we implement SKaR (Simultaneous kinetics and ringdown) technique, which is reported by Brown S.S.[5] As indicated by its name, SKaR is an approach where the entire reaction is monitored during each intensity decay within the high finesse cavity. At present we are monitoring reaction kinetics of CN in the flow by probing the loss of CN(v=1) by reaction with co-reactants such as propene, propane, and O2. These reactions are ideal candidates for validating the limits of coupling UF-CRDS with SKaR approach as there has been extensive studies published on these systems in CRESU where loss of CN(v=0) is probed by laser induced fluorescence spectroscopy [6,7].

1. N. Suas-David, S. Thawoos, and A. G. Suits, The Journal of Chemical Physics 151 (2019) 24420.

2. J. M. Oldham et al., The Journal of Chemical Physics 141 (2014) 154202.

3. C. Abeysekera et al., Review of Scientific Instruments 85 (2014) 116107

4. B. Rowe et al., The Journal of Chemical Physics 80 (1984) 4915.

5. S. S. Brown, A. Ravishankara, and H. Stark, The Journal of Physical Chemistry A 104 (2000) 7044

6. I. Sims et al., The Journal of Chemical Physics 97 (1992) 8798

7. S. B. Morales et al., Faraday Discussions 147 (2010) 155.