STATE-RESOLVED, 3-DIMENSIONAL PRODUCT RECOIL VELOCITY SPECTROSCOPY

We describe a conceptually and experimentally simple approach for quan tum-state-resolved measurement of the full three-dimensional recoil ve locity distribution of the products from photodissociation or photoini tiated chemical reaction. The method uses pulsed lasers to determine t wo components of the recoil velocity vector, by spatial displacement o f a probe laser beam relative to a photolysis laser beam, so we call t his method POSTS, for position sensitive translational spectroscopy. T he third component of the velocity vector is obtained from Doppler sel ection, ion time-of-flight mass spectrometry, spatial masking of a det ector, or use of a one-dimensional array detector. POSTS requires only a single probe laser, and it is not essential that this laser have a narrow frequency bandwidth. Its TOF measurements can be made with very high resolution on a spatial scale as small as 0.1 cm. POSTS will wor k with all atomic and molecular species having any magnitude of recoil velocity, and with most pulsed-laser detection techniques. We demonst rate the capabilities of the POSTS method by velocity measurements on the H atoms from photodissociation of HI, and HCL molecules from the v ibrational predissociation of (HCl)(2). In the latter case the high re solution capabilities of POSTS allow a determination of the bond disso ciation energy of the HCl dimer to an accuracy of +/-1 cm(-1) from. TO F measurements on a spatial scale of only 0.1 cm. (C) 1996 American In stitute of Physics.