Implementation of Time-Resolved Step-Scan Fourier Transform Infrared (FT-IR) Spectroscopy Using a kHz Repetition Rate Pump Laser

• Type of Material: Article
• Authors: Donny Magana, Emory University; Dzmitry Parul, Emory University; Brian Dyer, Emory University; Andrew P. Shreve, Los Alamos National Laboratory
• Language: English
• Date: 2011-05
• Publisher: SAGE Publications (UK and US)
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2011 Society for Applied Spectroscopy
• Title of Journal or Parent Work: Applied Spectroscopy
• ISSN: 0003-7028
• Volume: 65
• Issue: 5
• Start Page: 535
• End Page: 542
• Grant/Funding Information: This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility (A.P.S.). Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.; We acknowledge support from the Department of Energy through the Los Alamos National Laboratory LDRD program (D.M., R.B.D.) and the National Institute of General Medical Science, Grant GM068036 (D.P., R.B.D.).
• Keywords: Spectroscopic instrumentation; Infrared spectroscopy; FT-IR spectroscopy; Time-resolved spectroscopy; Time-resolved step-scan Fourier transform infrared spectroscopy; Nanosecond phenomena
• Research Categories: Chemistry, General

Abstract

Time-resolved step-scan Fourier transform infrared (FT-IR) spectroscopy has been shown to be invaluable for studying excited-state structures and dynamics in both biological and inorganic systems. Despite the established utility of this method, technical challenges continue to limit the data quality and more wide ranging applications. A critical problem has been the low laser repetition rate and interferometer stepping rate (both are typically 10 Hz) used for data acquisition. Here we demonstrate significant improvement in the quality of time-resolved spectra through the use of a kHz repetition rate laser to achieve kHz excitation and data collection rates while stepping the spectrometer at 200 Hz. We have studied the metal-to-ligand charge transfer excited state of Ru(bipyridine)3Cl2 in deuterated acetonitrile to test and optimize high repetition rate data collection. Comparison of different interferometer stepping rates reveals an optimum rate of 200 Hz due to minimization of long-term baseline drift. With the improved collection efficiency and signal-to-noise ratio, better assignments of the MLCT excited-state bands can be made. Using optimized parameters, carbonmonoxy myoglobin in deuterated buffer is also studied by observing the infrared signatures of carbon monoxide photolysis upon excitation of the heme. We conclude from these studies that a substantial increase in performance of ss-FT-IR instrumentation is achieved by coupling commercial infrared benches with kHz repetition rate lasers.