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

Abstract

Solid para-H₂ doped with CH₃F at 1.8 K is studied in the ν₃ region (∼1040 cm⁻¹) using a quantum cascade laser source. Residual ortho-H₂ gives rise to distinct spectral features due to CH₃F–(ortho-H₂)_N clusters with N = 0, 1, 2, etc. The laser power (∼30 mW) is sufficient to significantly affect the sample, enabling novel photochromism experiments to be performed on a solid para-H₂ 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.