Time Resolved Infrared Spectroscopy (TRIR)

Time Resolved Infrared Spectroscopy

The time resolved infrared system is very similar to the TRO system. The pump source is either the 308 nm output of a XeCl excimer laser or the 355 nm output of a Nd:YAG laser. The probe source is one of four infrared lead salt diode lasers that are mounted in a helium cooled laser cold head. The lasers can be collectively tuned to cover the region between 2150 cm-1 to 1550 cm-1. A Digikrom 240 monochromator is used to exclude neighboring modes that are outside the region of interest. The pump and probe lasers are overlapped at the plane of the sample cell to maximize the amount of intermediate detected. The transmitted intensity of the infrared probe beam is incident on a Santa Barbara Research Center Hg/Cd/Te (MCT) photovoltaic detector, amplified, and recorded by a digital oscilloscope. A LabView Software interface written specifically for LeCroy WaveRunner oscilloscopes collects, parses and averages individual acquisitions. Typical concentrations of sample solutions are several mM. The optimal concentration depends upon the extinction coefficients at both 355 nm (or 308 nm) and in the infrared region. Solutions are equilibrated with gas mixtures on a vacuum line and then either transferred to gas tight syringes or directly to a modified Parr bomb calorimeter. In the latter case solutions are subsequently equilibrated with higher pressures of gas. A Sage 341B syringe pump or the elevated gas pressure in the Parr bomb is used to flow the solution through the IR cell. Click here to see an animation showing TRIR monitoring of a reaction.

Step-scan FTIR

The step-scan FTIR (BioRad FTS 60A/896) instrument at Los Alamos National Laboratories in collaboration with Jon Schoonover has provided an especially effective alternative to generating time-resolved spectra in a point by point fashion in the infrared region. Briefly, the mirrors of the interferometer in the FTIR spectrometer are moved in a periodic fashion as to effect steps in the path length difference between the arms of the interferometer. At each step a transient is collected with a sampling interval of typically 200 ns. Thus an array of interferograms is generated from which transient spectra from 1250 cm-1 to 2250 cm-1 for selected time intervals are extracted. A typical spectrum (the best we have) is shown to the right.

High Pressure TRIR Flow System


Time Resolved Infrared Spectroscopy

The time resolved infrared system is very similar to the TRO system. The pump source is either the 308 nm output of a XeCl excimer laser or the 355 nm output of a Nd:YAG laser. The probe source is one of four infrared lead salt diode lasers that are mounted in a helium cooled laser cold head. The lasers can be collectively tuned to cover the region between 2150 cm-1 to 1550 cm-1. A Digikrom 240 monochromator is used to exclude neighboring modes that are outside the region of interest. The pump and probe lasers are overlapped at the plane of the sample cell to maximize the amount of intermediate detected. The transmitted intensity of the infrared probe beam is incident on a Santa Barbara Research Center Hg/Cd/Te (MCT) photovoltaic detector, amplified, and recorded by a digital oscilloscope. A LabView Software interface written specifically for LeCroy WaveRunner oscilloscopes collects, parses and averages individual acquisitions. Typical concentrations of sample solutions are several mM. The optimal concentration depends upon the extinction coefficients at both 355 nm (or 308 nm) and in the infrared region. Solutions are equilibrated with gas mixtures on a vacuum line and then either transferred to gas tight syringes or directly to a modified Parr bomb calorimeter. In the latter case solutions are subsequently equilibrated with higher pressures of gas. A Sage 341B syringe pump or the elevated gas pressure in the Parr bomb is used to flow the solution through the IR cell. Click here to see an animation showing TRIR monitoring of a reaction.


Step-scan FTIR
The step-scan FTIR (BioRad FTS 60A/896) instrument at Los Alamos National Laboratories in collaboration with Jon Schoonover has provided an especially effective alternative to generating time-resolved spectra in a point by point fashion in the infrared region. Briefly, the mirrors of the interferometer in the FTIR spectrometer are moved in a periodic fashion as to effect steps in the path length difference between the arms of the interferometer. At each step a transient is collected with a sampling interval of typically 200 ns. Thus an array of interferograms is generated from which transient spectra from 1250 cm-1 to 2250 cm-1 for selected time intervals are extracted. A typical spectrum (the best we have) is shown to the right.
High Pressure TRIR Flow System