Liquid nitrogen cooled ccd detector

The RR measurements were carried out as previously described.^{1 (link)} Briefly, the 413.1 nm excitation from a Kr ion laser (Spectra-Physics, Mountain View, CA) was focused to an ~30 μm spot on the spinning quartz cell rotating at ~1000 rpm. The scattered light, collected at a right angle to the incident laser beam, was focused on the 100 μm wide entrance slit of a 1.25 m Spex spectrometer equipped with a 1200 grooves/mm grating (Bausch & Lomb, Analytical Systems Division, Rochester, NY), where it was dispersed and then detected by a liquid nitrogen-cooled CCD detector (Princeton Instruments, Trenton, NJ). A holographic notch filter (Kaiser Optical Systems, Ann Arbor, MI) was used to remove the laser line. The Raman shifts were calibrated with indene. The laser power was adjusted by neutral density filters, and the power at the sample point was measured by a handheld laser power meter (LaserCheck, Coherent Inc., Santa Clara, CA).
The IR spectra were recorded at 4 cm⁻¹ resolution on an FTIR instrument (Magna-IR 560, Nicolet, Madison, MI) with a CaF₂ IR cell (200 μm path). For the IR dark–light experiments, the 413.1 nm laser beam was introduced into one end of an optical fiber, and the IR cell surface (~1 cm diameter) was illuminated by the laser beam dispersed from the other end of the optical fiber.

The resonance Raman spectra were obtained as previously described (35 (link)). Briefly, the 413.1 nm excitation from a Kr ion laser (Spectra-Physics, Mountain View, CA) was focused to a ∼30 μm spot on the spinning quartz cell rotating at ∼ 1000 rpm. The scattered light, collected at a right angle to the incident laser beam, was focused on the 100 μm-wide entrance slit of a 1.25 m Spex spectrometer equipped with a 1200 grooves/mm grating (Bausch & Lomb, Analytical Systems Division, Rochester, NY), where it was dispersed and then detected by a liquid nitrogen-cooled CCD detector (Princeton Instruments, Trenton, NJ). A holographic notch filter (Kaiser Optical Systems, Ann Arbor, MI) was used to remove the laser line. The Raman shifts were calibrated with indene. The concentration of enzyme was 50 μM. The laser powers used for all Raman measurements are indicated in the captions.