NIR Raman spectrometer for monitoring protonation reactions in gaseous hydrogen

Spontaneous Raman spectroscopy was used to monitor molecular hydrogen isotope exchange reactions between H2, D2, and HD. A tunable 780 nm, multimode laser diode with power output between 300 and 500 mW served as the excitation source. Hydrogen isotopes could be detected at partial pressure of 13 Pa (number density 3.2 × 1021 m−3) at total gas pressure of 5.3 × 104 Pa (number density 1.3 × 1025 m−3) with signal-to-noise better than 2 during minutes long observations. The high sensitivity was achieved using multiple pass cell in conjunction with atomic vapor Rb absorption filter employed to eliminate Rayleigh scattered laser light. We have used the new spectrometer to measure the rapid isotope exchange reactions taking place in the palladium hydrogen purifier.