Infrared matrix-isolation spectroscopy using pulsed deposition of p-H2

We employed pulsed deposition of p-H2 onto a cold target to form a matrix sample suitable for measurements of infrared absorption. Unlike the method of rapid vapor deposition at approximately 2.5 K, developed by Fajardo et al., this method can be performed at a temperature as high as 5.5 K, achievable with a closed-cycle refrigerator; pumping on liquid helium in a cryostat is eliminated. Compared with the enclosed-cell method developed by Oka, Shida, Momose, and co-workers, this method is more versatile in sample preparation, especially for samples at a greater concentration or with high reactivity. Two experiments were tested: the pulse-deposited sample of CH4/p-H2 yields an infrared absorption spectrum nearly identical to that recorded with rapid vapor deposition, and a sample of vinyl chloride (C2H3Cl) in solid p-H2 irradiated with laser emission at 193 nm yields C2H5, in contrast to formation of HCl, C2H2, and a complex of HClC2H2 observed upon photolysis of C2H3Cl in an Ar matrix. These experiments are also compared with those with n-H2 or Ne as the matrix host.