Schematic of the ELISA electrostatic storage ring in combination with a laser system. The photofragment yield was obtained as a function of wavelength from the signal of neutrals hitting the detector.
Electrospray ion source used in the experiments. Ions are accumulated in a 22-pole ion trap in which they ascertain the temperature of the helium buffer gas (room temperature).
Time spectra of (a) ions after no photoexcitation, (b) ions after 500 nm photoexcitation, and (c) ions after 500 nm photoexcitation. The solid curve in (a) is an exponential fit to the data which gives a lifetime of the ions in the ring of 0.3 s. In (b) and (c) the solid lines are fits of three exponentials to the data. In both cases, the exponential decay with the longest time constant corresponds to the decay of ions in the ring after no photoexcitation. Lifetimes associated with the decays are 0.2 ms, 8 ms, and 0.3 s for ions, and 0.07 ms, 0.4 ms, and 0.2 s for ions. The structure of is shown in (b), while in (c) it can be seen that the iron atom in is moved slightly out of the heme plane (black bar).
(a) Ratio of the number of photoexcited ions (480 nm) that decay with a rate associated with the smallest time constant (0.1 ms), , to those that decay on a longer time period (7 ms), , as a function of the laser-pulse energy. The linear dependence is shown with a red line. (b) The ratio for photoexcited ions (528 nm), where the time constants are 0.08 and 8 ms, respectively. Here the ratio is constant, as indicated by the red line. The insets show the dependence of the number of photofragments from photoexcited ions that decay with a rate associated with the smallest time constant (closed squares) and those which decay on a longer time period (open squares) as functions of laser-pulse energy. In inset (a) a linear fit to the open squares (blue line) and a fit to the closed squares (green line), which gave a dependence to the pulse energy of power 2, are shown. In inset (b) a linear fit for each data set is shown.
Absorption spectra of (hollow circles) and (filled circles) in vacuo. Both one- and two-photon absorptions contributed to the number of photoexcited ions in the case of . However, only the photoexcited ions which result purely from one-photon absorption are shown here (see main text). For , absorption is due to one-photon absorption. The absorption spectrum of in solution is shown as a dashed blue curve. An enlarged view of the Q-band is shown in the inset. Curves were drawn to guide the eye, green and red representing and , respectively.
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