UV, extreme

Be is a very interesting element, produced by spallation of galactic cosmic rays. The only two usable lines are in the extreme UV (313 nm), in a crowded spectral region, and the stellar radiation is heavily absorbed by the earth s atmosphere, so that their observations are challenging in faint stars. Only very recently (Pasquini et al. 2004) the first Be observations became available, in 2 TO stars of the nearby NGC6397. 

Experiments on board the NASA Long Duration Exposure facility have been performed with spores from the bacterium Bacillus subtilis, allowing them to be exposed to the extreme conditions of space. Low pressures and highly energetic particles are dominant in space and most importantly around the Sun, including an intense UV radiation field. It is the latter that is the most destructive in terms of viability of the spores, and under controlled conditions the extreme UV exposure is four orders of magnitude more likely to kill the cells than when screened. Crucially, however, not all spores were killed. Protection of the spores from the UV field for example within the interior of the meteorite suggests that the spores... 

However, again this application did not succeed. Optical lithography continues. First by steppers with half or third spacing. Now, a new form of lithography is close to implementation, known as extreme-UV lithography. This uses coherent UV from a plasma of Sn4+ ions, which emits at around 100 eV. 

Several galaxy clusters show also an emission of extreme UV (Lieu et al. 1996, Durret et al. 2002) and soft X-ray (Bonamente et al. 2002, Kaastra et al. 2002) radiation in excess w.r.t. the thermal bremsstrahlung emission. This EUV emission excess may be consistent with both ICS of CMB photons off a non-thermal electron population (e.g., Lieu et al. 1999, Bowyer 2000) with Ee = 608.5 MeV (hv/keV)1/2 149 MeV for hv 60 eV, and with thermal emission from a warm gas at ksTe V 1 keV (Bonamente et al. 2002). In the case of Coma, the simple extrapolation of the ICS spectrum which fits the HXR excess down to energies 0.25 keV does not fit the EUV excess measured in Coma because it is too steep and yields a too high flux compared to the measured flux by the EUV satellite in the 0.065 — 0.245 keV band (Ensslin Biermann 1998). Thus, under the assumption that the HXR and the EUV emission of Coma is produced by ICS of CMB photons, the minimal requirement is that a break in the electron spectrum should be present in the range 0.3 — 2.8 GeV in order to avoid an excessive EUV contribution by the ICS emission and to be consistent with the radio halo spectrum. 

Although photochemical reactions of hydrogen and hydrocarbons proceed easily and with high quantum yields, nitrogen photochemistry is not that straightforward. The triple bond within the N2 molecule is extremely difficult to break (E> 9.7 eV). Furthermore, there are no optically allowed excitation paths into repulsive electronic excited states, and dissociation can occur only via indirect paths. Solar radiation below 100 nm can excite predissociating electronic states and constitutes a minor source of N atoms. Dissociative ionization of N2 by either electron impact or solar extreme UV (10-121 nm) radiation produces one N atom and one N+ ion [9] ... 

The recent detection of the [Nell] line emission at 12.81 pm from several disks by the Spitzer Space Telescope (e.g. Pascucci et al. 2007) has confirmed theoretical predictions that the disk atmosphere is heavily ionized and superheated, either by X-rays (Glassgold et al. 2007) or by extreme UV irradiation (Pascucci et al. 2007). However, X-rays and cosmic-ray particles (CRPs) may not be able to penetrate further toward the mid-plane of the planet-forming disk zone (r 3-20 AU), which makes the mid-plane essentially neutral and thus stable against accretion ( Dead Zone Gammie 1996 Dolginov Stepinski 1994). 

From an inspection of the UV absorption curves and the spectrum of terrestrial sunlight (Figure l) it is obvious that PET and PmPiPA strongly absorb part of the shortwave UV component of sunlight. Pure PP on the other hand does not itself absorb beyond 190 nm, so that it should be extremely UV stable. 

The resulting model atmospheres differ considerably between each other in the extreme UV. This has a strong impact on the predicted nebular ionization structure (see e.g. Stasinska Schaerer 1997 for the Ne and the N+/() 1 problems). Actually, the confrontation of photoionization models with observations of nebulae is expected to provide tests of the ionizing fluxes from model atmospheres (see Oey et al. 2000, Schaerer 2000, Giveon et al. 2002, Morisset et al. 2002). This is especially rewarding with the ISO data which provide accurate measurements for many fine-structure lines of adjacent ions. 

Applying the same idea to the activation of an aliphatic C-H bond would be a major goal, but is not as simple as one may hope. Direct irradiation of the precursor can not be contemplated because simple aliphatic derivatives do not absorb at convenient wavelengths (i.e. those at which efficiently emitting lamps are available), but only in the extreme UV. At any rate, even when the way to reach the excited state is found, more than one chemical (fragmentation) path is usually available, making the process less clean that it may be desired. However, the use of photocatalysts may help, particularly for reactions via aliphatic carbon-centered radicals. 

Detection of Extreme UV and Soft X-Rays with MicroChannel Plates A Review... 

Multichannel Extreme UV Spectroscopy of High Temperature Plasmas... 

Figure 1. Extreme UV (EUV) spectrum, from the PDX tokamak, showing prominent impurity emission lines. (Reproduced with permission from Ref. 12. Copyright 1982,...

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