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%\title{High-Resolution Spectroscopy in Argon using a Long-Pulse Fourier-Transform Limited Laser System}
\title{EXPLORING THE RESOLUTION LIMIT OF PFI-ZEKE PHOTOELECTRON SPECTROSCOPY}
%HIGH-RESOLUTION SPECTROSCOPY IN ARGON USING A LONG-PULSE FOURIER-TRANSFORM LIMITED LASER SYSTEM}

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\author{\underline{\FirstName H. \LastName HERBURGER}, \FirstName V. \LastName WIRTH,
\FirstName U. \LastName HOLLENSTEIN, \FirstName F. \LastName MERKT}
\address{Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland}

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\fancyhead[C]{{\footnotesize \textit{HRMS, 28th Colloquium, Dijon, France,
			Aug. 28 - Sept. 1, 2023}}}
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\begin{document} 
 \maketitle 
The spectral resolution in pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy is related to the state selectivity in the diabatic ionisation of the Rydberg states by time-dependent electric fields. The selectivity is determined by the applied electric-field pulse sequence.
Hollenstein \textit{et al.}\footnote{U.\,Hollenstein, R.\,Seiler, H.\,Schmutz, M.\,Andrist, and F.\,Merkt, {\em J. Chem. Phys.} {\bf 115}, 5461--5469 (2001).} used discrete electric-field pulses with increasing field strength in combination with a preceding field pulse of opposite polarity and achieved a spectral resolution of 0.06\,cm$^{-1}$.
To improve the resolution further, Harper \textit{et al.}\footnote{Oliver\,J.\,Harper, Ning\,L.\,Chen, S\'everine\,Boy\'e-P\'eronne, and B\'erenger\,Gans, {\em Phys. Chem. Chem. Phys.} {\bf 24}, 2777--2784 (2022).} recently replaced the sequence of field steps by a linearly increasing field, as used earlier by Reiser \textit{et al.}\footnote{ G.\,Reiser, W.\,Habenicht, K.\,M\"uller-Dethlefs, and	E.\,W.\,Schlag, {\em Chem. Phys. Lett.} {\bf 152}, 119--123 (1988).}, in combination with a prepulse of opposite polarity and obtained promising results on the PFI-ZEKE photoelectron spectrum of NO and CO$_2$. They called this new method pulsed-ramped field-ionisation (PRFI)-ZEKE photoelectron spectroscopy.
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Using a home-built narrow-bandwidth long-pulse laser system (pulse lengths up to 50\,ns, bandwidth$<50$\,MHz) in combination with a pulsed field ramp,$^{2, 3}$ we explore the resolution limit of this approach. To avoid overlap of spectral lines, we chose the atoms Ar, Kr, and Xe as test systems and recorded PRFI-ZEKE photoelectron spectra of transitions from the metastable state ($n$p)$^5$($(n+1)$s)$[3/2]_2$ $\left(^3\mathrm{P}_2\right)$ of the neutral rare-gas atom to the ($n$p)$^5$ $^2$P$_{3/2}$ state of the corresponding ion, with $n=3$, 4, 5 for Ar, Kr, and Xe, respectively.
%This system also offers the advantage of precisely known ionisation energies\footnote{V.\,L.\,Sukhorukov, I.\,D.\,Petrov, M.\,Sch\"afer, F.\,Merkt, M.-W.\,Ruf, and H.\,Hotop, {\em J. Phys. B: At. Mol. Opt. Phys.} {\bf 45}, 092001 (2012) and references therein.} with which the ionisation energies determined with the new method are compared.
We present PRFI-ZEKE photoelectron spectra that exhibit both adiabatic and diabatic ionisation dynamics. The resolution of these spectra is improved to 0.05\,cm$^{-1}$ which constitutes the resolution record in photoelectron spectroscopy.$^1$
The determined ionisation energies are compared with precisely known literature values\footnote{V.\,L.\,Sukhorukov, I.\,D.\,Petrov, M.\,Sch\"afer, F.\,Merkt, M.-W.\,Ruf, and H.\,Hotop, {\em J. Phys. B: At. Mol. Opt. Phys.} {\bf 45}, 092001 (2012) and references therein.}.
The current resolution is limited by adiabatic field ionisation below $n= 190$ and by electric stray fields, which affect the field-ionisation dynamics above $n=190$. 
%PFI-ZEKE photoelectron spectra of argon were measured starting from the metastable states 3p$^5$4s$[3/2]_2$ $^3$P$_2$ and 3p$^5$4s$'[1/2]_0$ $^3$P$_0$,\footnote{V.\,L.\,Sukhorukov, I.\,D.\,Petrov, M.\,Sch\"afer, F.\,Merkt, M.-W.\,Ruf, and H.\,Hotop, {\em J. Phys. B: At. Mol. Opt. Phys.} {\bf 45}, 092001 (2012) and references therein.} which are presented to determine the spectral resolution limit of the used method.
\end{document}
