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Benzhydryl radicals and cations are reactive intermediates central to the under-standing of organic reactivity. They can be generated from benzhydryl halides by UV irradi-ation. We performed transient absorption (TA) measurements over the range from femto -seconds to microseconds to unravel the complete reaction scheme. The 290–720-nm proberange allows the unambiguous monitoring of all fragments. The appearance of the radical isdelayed to the optical excitation, the onset of the cation signal is found even later. Ab initiocalculations show that this non-rate behavior in the 100 fs range is due to wavepacket motionfrom the Franck–Condon region to two distinct conical intersections. The rise of the opticalsignal with a quasi-exponential time of 300 fs is assigned to the planarization and solvationof the photoproducts. The bond cleavage predominantly generates radical pairs. A subse-quent electron transfer (ET) transforms radical pairs into ion pairs. Due to the broad inter-radical distance distribution and the distance dependence, the ET is strongly non-exponen-tial. Part of the ion pairs recombine geminately. The ET and the recombination are terminatedby the depletion of close pairs and diffusional separation. The remaining free radicals and cations undergo further reactions in the nanosecond to microsecond regime.

The Pan-STARRS1 survey is collecting multi-epoch, multi-color observations of the sky north of declination −30° to unprecedented depths. These data are being photometrically and astrometrically calibrated and will serve as a reference for many other purposes. In this paper, we present our determination of the Pan-STARRS1 photometric system: g_P1, r_P1, i_P1, z_P1, y_P1, and w_P1. The Pan-STARRS1 photometric system is fundamentally based on the Hubble Space Telescope Calspec spectrophotometric observations, which in turn are fundamentally based on models of white dwarf atmospheres. We define the Pan-STARRS1 magnitude system and describe in detail our measurement of the system passbands, including both the instrumental sensitivity and atmospheric transmission functions. By-products, including transformations to other photometric systems, Galactic extinction, and stellar locus, are also provided. We close with a discussion of remaining systematic errors.

We have used a precision-calibrated photodiode as the fundamental metrology reference in order to determine the relative throughput of the PanSTARRS telescope and the Gigapixel imager, from 400 nm to 1050 nm. Our technique uses a tunable laser as a source of illumination on a transmissive flat-field screen. We determine the full-aperture system throughput as a function of wavelength, including (in a single integral measurement) the mirror reflectivity, the transmission functions of the filters and the corrector optics, and the detector quantum efficiency, by comparing the light seen by each pixel in the CCD array to that measured by a precision-calibrated silicon photodiode. This method allows us to determine the relative throughput of the entire system as a function of wavelength, for each pixel in the instrument, without observations of celestial standards. We present promising initial results from this characterization of the PanSTARRS system, and we use synthetic photometry to assess the photometric perturbations due to throughput variation across the field of view.