Dissociative ionization of ICl studied by ion imaging spectroscopy

TLDR: In this paper, the authors measured the speed and angular distribution of I+ ions, produced when ICl molecules were exposed to both ultraviolet and visible radiation at 304+608 nm, 355+664 nm, and 304+532 nm.

Abstract: The speed and angular distributions of I+ ions, produced when ICl molecules were exposed to both ultraviolet and visible radiation at 304+608 nm, 355+608 nm, and 304+532 nm, were measured by velocity map imaging. An intense central feature in the I+ images was observed to be very sensitive to the polarization of the ultraviolet light and is attributed to a dissociative ionization mechanism involving three-body fragmentation: ICl+hv (visible)+3hv (ultraviolet)→I++Cl+e−. The effect of varying the delay between the visible and ultraviolet radiation on the I+ images suggests that an intermediate gateway state of ICl reached by absorption of one photon of visible light mediates the transition to the superexcited dissociative ionization state.

Figures

FIG. 7. Time-resolved I1 signal intensity produced from ICl with nonresonant two-color radiation using wavelengths of~a! 355 and 608.04 nm and ~b! 304.40 and 532 nm. The horizontal axis is the delay time between the visible and ultraviolet laser pulses, where a negative delay time means that the visible pulse precedes the ultraviolet pulse.

FIG. 3. Two-dimensional~2-D! images of the I1 ions obtained from ICl by resonant one-color excitation at 304.02 nm, using the second harmonic of a dye laser tuned to a~211! REMPI transition of I* (2P1/2). The image was taken with the ultraviolet polarization (EUV) aligned perpendicular to the detection axis. The lower panel shows the velocity distribution of I* (2P1/2) calculated from the upper image.

FIG. 2. The I1 spectra from ICl in the two-color experiments, with~a! the ultraviolet ~UV! wavelength fixed at 355 nm while the visible wavelength was scanned, and with~b! the visible wavelength fixed at 532 nm and UV wavelength scanned. Vibrational assignments for theA 3P1(v8) ←X1S1(v9) transitions of I35Cl and I37Cl are discussed in Sec. IV C. The arrows indicate the wavelength at which the images shown in Fig. 6~a! were measured. I and I* denote the UV two-photon resonance-enhanced multiphoton signals for I(2P3/2) and I( 2P1/2), respectively. Assignments of these transitions are given in Ref. 12.