HIGHEST RESOLUTION FOURIER TRANSFORM INFRARED SPECTROSCOPY WITH AN ELEVEN CHAMBER BRUKER INTERFEROMETER AT THE SWISS SYNCHROTRON
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Date
2010
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Ohio State University
Abstract
We have interfaced a newly constructed eleven chamber interferometer, the ETH-SLS Bruker IFS 125 HR prototype 2009, to the infrared port available at the Swiss Light Source (SLS), located at the Paul-Scherrer-Institute. The Maximum Optical Path Difference (MOPD) of this spectrometer is 11.70~m allowing for a best theoretical unapodized resolution of 0.00053~cm$^{-1}$ (18~MHz). The ETH-SLS Bruker spectrometer is a further development of our nine chamber interferometer Bruker IFS 120/125 Zurich prototype 2001, \textbf{2003}, \emph{84}, 177.}$^,$, \textbf{2007}, \emph{8}, 1271.} which has an MOPD of 9.4~m and unapodized resolution of 0.00068~cm$^{-1}$ (23~MHz). We present spectra of CO and pyrimidine (C$_4$H$_4$N$_2$) as examples to illustrate the improved resolution. Due to the high brightness of the synchrotron source the signal-to-noise ratio is effectively 5 to 20 times better than that of conventional thermal sources in the spectral region between 180 and 900~cm$^{-1}$ (6-28 THz). We present examples of pyrimidine (C$_4$H$_4$N$_2$) and CDBrClF spectra in the region 600 to 900~cm$^{-1}$ and of phenol (C$_6$H$_5$OH) and aniline (C$_6$H$_5$NH$_2$) spectra in the region 180 to 350~cm$^{-1}$. Due to the excellent resolution and the bright synchrotron source we were able to detect the spin statistical weights in the pyrimidine, \textbf{2007}, \emph{243}, 280.} spectra and found new combination bands in the CDBrClF spectra. We were able to rotationally resolve the torsional $c$-type band of phenol with $\nu_{0a}=309.1141$~cm$^{-1}$ and $\nu_{0b}=309.5517$~cm$^{-1}$ and detect a torsional splitting of 0.4376~cm$^{-1}$ in the $v=1$ torsional level. In addition, we were able to rotationally resolve and assign the very weak two torsional $b$-type subbands of aniline with $\nu_{0a}=234.8$~cm$^{-1}$ and $\nu_{0b}=304.3$~cm$^{-1}$ showing the mode selective inversion splitting, \textbf{1998}, \emph{298}, 320.}.
Description
Author Institution: Physical Chemistry, Eth Zurich, CH-8093 Zurich, Switzerland; Swiss Light Source, Paul-Scherrer-Institute, CH-5232 Villigen, Switzerland ; Bruker Optics, D-76275 Ettlingen, Germany