A perspective on chemistry in transient plasma from broadband rotational spectroscopy.

Daniel P. Zaleski,Nicholas R. Walker,Susanna L. Stephens

doi:10.1039/c4cp04108a

Abstract

Broadband rotational spectroscopy provides a new method by which plasma chemistry can be explored. Molecules and complexes form when precursors within an expanding gas sample are allowed to interact with plasma generated by an electrical discharge or laser vaporisation of a solid. It is thus possible to selectively generate specific molecules or complexes for study through a careful choice of appropriate precursors. It is also possible to survey an extensive range of the products formed under a given set of initial conditions in an approach termed "broadband reaction screening". Broadband rotational spectroscopy provides an opportunity to simultaneously monitor the transitions of many different chemical products and this allows broader details of reaction pathways to be inferred. This Perspective will describe various experimental approaches and review recent works that have applied broadband rotational spectroscopy to study molecules and complexes generated (in whole or in part) through chemistry occurring within transient plasma.

Highlights

The earliest experiments in microwave spectroscopy probed chemical samples under thermal equilibrium and demonstrated the value of pure rotational spectroscopy for the characterisation of molecular structure.[1,2,3,4,5] The subsequent development of the Balle–Flygare Fourier transform microwave (BF-FTMW) spectrometer[6] introduced a step-change in the capabilities of spectrometers operating at microwave frequencies
chirped-pulse FTMW (CP-FTMW) spectroscopy is a comparatively recent addition to a long list of spectroscopic techniques that have been applied to study molecules and complexes generated in this way.[31,32,33,34]
Fourier transform microwave spectroscopy can generally be performed at high resolution such that transitions are recorded with typical FWHM of less than 150 kHz

Summary

Introduction

The earliest experiments in microwave spectroscopy probed chemical samples under thermal equilibrium and demonstrated the value of pure rotational spectroscopy for the characterisation of molecular structure.[1,2,3,4,5] The subsequent development of the Balle–Flygare Fourier transform microwave (BF-FTMW) spectrometer[6] introduced a step-change in the capabilities of spectrometers operating at microwave frequencies. This Perspective will review how broadband rotational spectroscopy has recently been employed to characterise chemical products generated entirely or partially within transient plasma accompanying laser vaporisation of a solid material or electrical discharge through a gas sample.

Results

Conclusion