Deceleration and trapping of polyatomic molecules

Manish Vashishta

Published Jan 1, 2020• 0 citations

Abstract

In this dissertation, substantial headway towards the Zeeman deceleration and magnetic trapping of methyl radicals, and AC Stark trapping of ammonia are presented. Notably, the first ever trapping of gaseous methyl radicals within a permanent magnetic trap is discussed in detail. Additionally, the use of a counter rotating nozzle to produce slow polyatomic molecular beam is discussed. The methyl radical is the smallest and most stable paramagnetic intermediate hydrocarbon species, and as such, the physicochemical properties of this species are of substantial interest to astrochemists and organic chemists alike. Methyl radical, being a paramagnetic molecule, is decelerated using an 85 coil Zeeman decelerator from 320 m/s to 60 m/s. Notably, the first ever trapping of methyl radicals in the gas phase inside a permanent magnetic trap is described here. The trapped radicals had a temperature of 200 mK, and a lifetime of greater than one second. Lastly, the collisional loss cross sections for the methyl radical with helium and argon are also reported. In addition to the magnetic trapping of the methyl radical, progress towards the trapping of polar molecules with microwave radiation is discussed in detail. A quality (abbr. Q) factor of 5 x 105 was achieved by cooling a Fabry Perot cavity with superconducting mirror surfaces to 3 K. Resulting from the large Q factor, the maximum electric field inside the cavity is 1 MV/m when a power input of 10 W is used. At this electric field, ammonia molecules travelling slower than 10 m/s can be successfully trapped. Additionally, the AC stark shift of ammonia molecules within the trap is reported as the first step towards their trapping. Lastly, a counter rotating nozzle was constructed based on the design presented by Strebel et al. at the University of Freiburg. The technical modifications presented in this thesis yielded an increase in the density of the molecular beam by two orders of magnitude, in comparison to the Freiburg design. This nozzle was used to decelerate acetone from 430 m/s to 110 m/s, and unlike the Stark and Zeeman decelerators, it can be used to decelerate any gaseous molecules.

DOI: 10.14288/1.0390918

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