Infrared photochromism in a quantum crystal: laser pumping and probing in solid para-H2 doped with CH3F

Solid para-H-2 doped with CH3F at 1.8 K is studied in the nu(3) region (similar to 1040 cm(-1)) using a quantum cascade laser source. Residual ortho-H-2 gives rise to distinct spectral features due to CH3F-(ortho-H-2)(N) clusters with N = 0, 1, 2, etc. The laser power (similar to 30 mW) is sufficient to significantly affect the sample, enabling novel photochromism experiments to be performed on a solid para-H-2 matrix-isolated sample. It is found that population can be reversibly transferred between the N = 1 line and satellite features close to the N = 0 line.