A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. I. The low-temperature flow system

Abstract

We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator. Uniform flows at temperatures as low as 20 K were readily achieved with only modest pumping requirements, as demonstrated by impact pressure measurements and pure rotational spectroscopy. The proposed technique will be suitable for application in diverse fields including fundamental studies in spectroscopy, kinetics, and reaction dynamics. © 2014 AIP Publishing LLC.

Development of a pulsed uniform supersonic gas expansion system based on an aerodynamic chopper for gas phase reaction kinetic studies at ultra-low temperatures

“…In a recent publication, they presented results of collisional quenching of NO(A 2 Σ + , v ′ = 0) by NO(X 2 Π) and O 2 at temperatures as low as 34 K (Sánchez-Gónzalez et al, 2014). Following a different direction, Oldham et al (2014) developed a new method for pulsing a gas. This was based on a fast high-throughput pulsed valve driven by a piezoelectric stack actuator and is presently applied to microwave spectroscopy measurements at temperatures down to 22 K.…”

“…Laval nozzles are important tools in other fields such as powder metallurgy, including gas-assisted atomization (Allimant et al, 2009 andSi et al, 2014), narrow size nanoparticle synthesis (Li et al, 2008 andJung et al, 2008), or inertial separation of particles (Kanaoka et al, 2001). These type of nozzles can be found as well as part of apparatuses developed for studies concerning spray deposition (Jen et al, 2006), formation of super thin fibers (Blim et al, 2014), hydrogen production (Du et al, 2012), laser cutting (Man et al, 1999), homogeneous or binary nucleation (Kim et al, 2004 andTanimura et al, 2010), infrared (Tanimura et al, 1996 andBenidar et al, 2000) or microwave spectroscopy (Oldham et al, 2014), or hypersonic astrophysical jets simulations (Tordella et al, 2011).…”

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics

“…20 The flow system has been developed and integrated into a new CP-FTMW spectrometer operating in the K a -band (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40). 20 We term this combination a Chirped-PulseUniform Flow (CPUF) spectrometer. The system is also used with a mm-Wave spectrometer (60-90 GHz) based on one developed in the Field group 8, 11 but its performance is not described in this report.…”

Product Branching in the Low Temperature Reaction of CN with Propyne by Chirped-Pulse Microwave Spectroscopy in a Uniform Supersonic Flow

“…8,36 A broadband frequency chirp (in the 6090 GHz region) is broadcast into the pulsed uniform flow at a series of intervals after a laser fires to initiate the reaction. All molecules with a dipole moment and with rotational transitions in the scanned frequency range are polarized by the radiation.…”

“…7,8 This technique, relying on chirped-pulse Fourier-transform microwave spectroscopy, 9−15 provides clear quantifiable spectroscopic signatures of polyatomic products in bimolecular or unimolecular reactions for virtually any species with a modest electric dipole moment.…”