Helium, resonance spectrum

Fig. 10. Photoeleotron spectrum of oxygen using the helium resonance line (21-21 e.v.) obtained with a magnetic electron energy analyser (May and Turner, unpublished work). Ionization energy increasing from left to right. The spectrum reveals four levels of ionization and the vibrational structure associated with each state of the ion can be clearly distinguished. This spectrum may be compared with that obtained using an electrostatic retarding field analyser (Al-Joboury et al., 1965).

Fio. 12. Fhotoelectron spectrum of methanol vapour using the helium resonance line (21-21 e.v.). Ionization energy increases from left to right. The adiabatic ionization potentials measured (Al-Jobomy and Turner, 1964) are indicated by vertical arrows, and can be compared with (probably) vertical I.P. values derived from electron impact appearance potentials by Collin (1961) (dotted arrows). 

A useful light source is the helium resonance lamp which produces light of wavelength 58.4 nm or a photon energy of 21.2 eV, enough to ionize any neutral molecule. Often several peaks can be observed in the photoelectron spectrum... 

Optical detection of magnetic resonance (ODMR) was attempted for measurements of the pH effects on the triplet state of purine to investigate the protonation site of purine at low temperatures (78JA7131). The ODMR spectrum did not show the presence of more than one triplet state at liquid helium temperatures. Since the protonated tautomers 1H,9H (3a) and H,1H (3b) have similar bond structures, their triplets should have similar zero-field parameters and are thus not easy to distinguish by ODMR. 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

The checkers used a 40-cm. spinning-band column. The product, n2bD 1.4237, was shown to be 98.9% pure by gas-liquid chromatography on a 6-ft. 20% fluorosilicone column. The retention time was 3.75 minutes with a flow rate of helium of 100 ml. per minute, and a column temperature of 125° with the injection port at 170°. The 19 F n.m.r. spectrum (56.4 MHz) consists of four lines of equal intensity centered at +3396 Hz from trichlorofluoromethane (internal) and two sets of two overlapping quartets centered at +4369 Hz and +4461 Hz, respectively. The integrated intensities of the three sets of fluorine resonances are 3 1 1. 

Figure 9. Resonance Raman spectrum of the 2Fe-2S-4Cys cluster In oxidized spinach ferredoxln. Protein ( 2 mM) maintained at 15 K In a helium Dlsplex and probed with 488.0 nm excitation. Spectral contribution of Ice In 220-320 cm" 1 region has been subtracted. (Data from Ref. 21). Starred features Indicate peaks Identified as totally symmetric Aig vibrations (23,24).

Calibration and EBIT spectra are fitted with Lorentzian convolved with slit profiles. The width of the Lorentzian and common slit components are free parameters in the fit. For calibration lines the background is negligible and not fitted. Helium-like resonances and the largest satellite are fitted with Lorentzian profiles convolved with slit profiles in addition to a constant background. Fig. 2 shows the result of profile fitting to a helium-like vanadium spectrum. 

Closer inspection of Fig. 10.8 reveals that the first three m series are completely isolated, i.e. the resonances with different m quantum numbers are energetically well separated from each other. But Fig. 10.8 (d) shows that the lowest state of the fifth series intrudes into the fourth series. The higher series are characterized by more and more intruder states. Thus, as conjectured in Section 10.1 on the basis of the simple independent-particle He -f e model, it is the onset of overlapping series with the accompanying intruder states that, on the quantum level, are the source of complicated behaviour in the helium spectrum. 

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