Photon, monochromatic

Photoelectron spectroscopy involves the ejection of electrons from atoms or molecules following bombardment by monochromatic photons. The ejected electrons are called photoelectrons and were mentioned, in the context of the photoelectric effect, in Section 1.2. The effect was observed originally on surfaces of easily ionizable metals, such as the alkali metals. Bombardment of the surface with photons of tunable frequency does not produce any photoelectrons until the threshold frequency is reached (see Figure 1.2). At this frequency, v, the photon energy is just sufficient to overcome the work function

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Technical Requirements. AXS requires an X-ray source with easily tunable, monochromatic photon wavelength. This means that a respective device can only be operated at a synchrotron. In general a 2D detector is used. 

The incident monochromatic photon-to-current conversion efficiency (IPCE), also called external quantum efficiency, is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. It is expressed in Equation (7).29 In most cases, the photoaction spectrum overlaps with the absorption spectrum of the sensitizer adsorbed on the semiconductor surface. A high IPCE is a prerequisite for high-power photovoltaic applications, which depends on the sensitizer photon absorption, excited state electron injection, and electron transport to the terminals ... 

Several approaches can be taken to minimize the effect of standing waves. Since the phenomenon results from coherent interference of monochromatic photons it can be reduced by employing broadband illumination. 

Tomita, M. Hieda, K. Watanabe, R. Takakura, K. Usami, N. Kobayashi, K. Hieda, M. Comparison between the yields of DNA strand breaks and ferrous ion oxidation in a Fricke solution induced by monochromatic photons, 2.147-10 keV. Radiat. Res. 1997,148,490 91. 

In photoelectron spectroscopy, a monochromatic photon beam impinges on a solid... 

An analogous behavior extends to other species having small reorganization energies and appropriate potentials such as the iron(II) complexes Fe(DMB)32 + and Fe(DTB)32 + (Ey2 0.95 V versus SCE). When used in the presence of an excess of Co(DTB)32 + and in conjunction with suitable sensitizers like the heteroleptic dye Ru(dnbpy)(H2DCB)22+ (Em = 1.25 V versus SCE) (Fig. 17.28), the iron(II) comediators clearly enhance the performance of the Co(DTB)32+ and outperform the I /I3 redox couple, at least in terms of monochromatic photon to current conversion efficiency, with maximum values close to 85%. 

The photoionization efficiency is defined as the number of ions, produced by one incident photon on unit path length at unit gas pressure. The curves in Figures 3-6 represent spectral efficiency curves. On them the ratio of the measured photocurrent to the number of incident monochromatic photons is plotted as function of the photon energy (in e.v.). At the low pressure used in the mass spectrometer (< 10 3 torr) the efficiency curves are proportional to the photoionization cross-section curves.3... 

In the formulation of mechanism we assume that the radicals -NH2, C6H5CH2-, CH2NH2, C6H5- are split off and subsequently photoionized by the monochromatic photons of the same energy of 10.15 e.v. 

Lasers generate a high-intensity output of monochromatic photon energy, and studies of the photochemical reactions induced by this have created a virtual subdivision of photochemistry known as laser chemistry While the output of a laser can heat, anneal, burn, cut. or be usedinstrumentally as a spectral source, we are concerned here only with those chemical effects attributable to the photon output at wavelengths between near infrared and near ultraviolet, i.e.. between about 12 and 0.2 microns. 

Folkard M, Prise KM, Vojnovic B, Brocklehurst B, Michael BD (2000) Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons an arrangement for irrdiating dry or hydrated DNA with monochromatic photons. Int J Radiat Biol 76 763-771 Folkard M, Prise KM, Turner CJ, Michael BD (2002) The production of single strand and double strand breaks in aqueous solution by vacuum UV photons below 10 eV. Radiat Prot Dosim 99 147-149 FoxRA, Fielden EM, SaporaO (1976) Yield of single-strand breaks in the DNA of E. coli 10 msec after irradiation. Int J Radiat Biol 29 391-394... 

For the photolysis experiments, a low pressure mercury lamp (12 W) from Helios Italquartz (Milan, Italy) was employed. The lamp emits monochromatic photons at about 245 nm. The UV irradiations were performed at room temperature in a quartz reactor fitted with inlet and outlet gas valves with the lamp inserted inside the reactor (Ninomiya and Naito 1989). All irradiations were performed under inert atmosphere with rigorous exclusion of air. These conditions were achieved by bubbling continuously Ar or He through the solutions. 

Besides its practical importance, photodissociation — especially of small polyatomic molecules — provides an ideal opportunity for the study of molecular dynamics on a detailed state-to-state level. We associate with molecular dynamics processes such as energy transfer between the various molecular modes, the breaking of chemical bonds and the creation of new ones, transitions between different electronic states etc. One goal of modern physical chemistry is the microscopical understanding of molecular reactivity beyond purely kinetic descriptions (Levine and Bernstein 1987). Because the initial conditions can be well defined (absorption of a single monochromatic photon, preparation of the parent molecule in selected quantum states), photodissociation is ideally suited to address questions which are unprecedented in chemistry. The last decade has witnessed an explosion of new experimental techniques which nowadays makes it possible to tackle questions which before were beyond any practical realization (Ashfold and Baggott 1987). 

IPCE Incident monochromatic photon-to-current conversion efficiency... 

The incident monochromatic photon-to-current conversion efficiency (IPCE) is plotted as a function of excitation wavelength. The IPCE value in the plateau region is 80% for complex 2, while for complex 25 it is only about 66%. In the red region, the difference is even more pronounced. Thus, at 700 nm the IPCE value is twice as high for the fully protonated complex 2 as compared to the deprotonated complex 25. As a consequence, the short circuit photocurrent is 18-19 mAcrn-2 for complex 2, while it is only about 12-13 mA cm-2 for complex 25. However, there is a trade-off in photovoltage, which is 0.9 V for complex 25, as compared to 0.65 V for complex 2. Nevertheless, this is insufficient to compensate for the current loss. Hence, the... 

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