Synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy of radicals produced in a flow tube: OH and OD

Abstract

We present a microwave discharge flow tube coupled with a double imaging electron/ion coincidence device and vacuum ultraviolet (VUV) synchrotron radiation. The system has been applied to the study of the photoelectron spectroscopy of the well-known radicals OH and OD. The coincidence imaging scheme provides a high selectivity and yields the spectra of the pure radicals, removing the ever-present contributions from excess reactants, background, or secondary products, and therefore obviating the need for a prior knowledge of all possible byproducts. The photoelectron spectra encompassing the X(3)Σ(-) ground state of the OH(+) and OD(+) cations have been extracted and the vibrational constants compared satisfactorily to existing literature values. Future advantages of this approach include measurement of high resolution VUV spectroscopy of radicals, their absolute photoionization cross section, and species/isomer identification in chemical reactions as a function of time.

A vacuum ultraviolet photoionization time‐of‐flight mass spectrometer with high sensitivity for study of gas‐phase radical reaction in a flow tube

“…In particular, photoionization efficiency spectra (PIES) corresponding to each mass are measured by scanning synchrotron photon energy and then their individual ionization energies (IEs) and structure‐specific information can be obtained . Recently, photoelectron photoion coincidence spectroscopy (PEPICO), analyzing both the photoion and the photoelectron from photoionization in coincidence, has been utilized at several synchrotron facilities to investigate radical reactions . The mass‐selected threshold photoelectron spectra with high‐energy resolution obtained from PEPICO offer greater selectivity than PIMS …”

Vacuum ultraviolet photoionization cross section of the hydroxyl radical

“…The photoionization spectroscopy of OH in the vacuum ultraviolet (VUV) near its first ionization threshold remains less studied. Past spectroscopic experiments of the OH radical in the VUV used photoelectron, [6][7][8][9][10] photoabsorption, 11 and photoionization [12][13][14] methods. Photoionization of OH(X 2 Π) in the threshold region removes an electron from the valence (2pπ) molecular orbital to form the ground electronic state of OH + (X 3 Σ ).…”

Pyrolysis of n-butane investigated using synchrotron threshold photoelectron photoion coincidence spectroscopy

“…Especially rather than the steps in the PIE spectra, electronic states even ne vibrational structures of ions can appear as distinct peaks in the mass-selected TPES and offer great selectivity and sensitivity. 3,[13][14][15] As a representative, the mass-selected TPES of the methyl radical, ethyl radical and propylene products from pyrolysis of n-butane were recorded with a 15 meV scanning step size in the energy range of 8.0-10.0 eV and are depicted in Fig. 4.…”

“…In recent years PEPICO as an efficient analytical approach has started to be applied in complex systems such as combustion and atmosphere chemistry to identify products and isomers. [13][14][15] The objective of the present study, n-butane is the prototype of hydrocarbons and an essential model fuel to study combustion behaviors. The thermal decomposition reactions of nbutane are important initiation steps in the high-temperature oxidation and strongly inuence on the ignition time, 16 which have attracted a lot of attention in the past decades.…”