Helium absorption spectrum

Fig. 3.12. The rototranslational absorption spectrum of H2-He pairs at three temperatures 77.4 K ( ), 195 K (x), and 293 K ( ). The data shown represent the enhancement of the absorption due to the addition of helium to hydrogen gas, obtained in 32 mole percent equilibrium hydrogen concentration in helium by subtraction of the H2-H2 spectra after [37].

Hydrogen-Helium Mixtures. Accurate ab initio dipole surfaces for both the rototranslational collision-induced absorption spectrum in the far infrared [280], and the rotovibrational collision-induced absorption spectrum in the near infrared [151], have been obtained that could have... 

Figure 11. Absorption spectrum of Pt(en)Cl2 in an aqueous 0.3M Cl solution and in single crystals with polarized light at 300° K and at liquid helium temperatures (nominally 15°K)...

Figure 5.9 The first spectrum is an absorption spectrum, it is composed of black lines on a continuous spectrum. The black lines correspond to certain frequencies absorbed by a given element, helium in this case. They can be matched to the colored lines present in helium s emission spectrum, shown below the absorption spectrum. 

Solid COj. Table V summarizes the available data for solid CO. The far infrared absorption spectrum in the lattice mode region was reported first by Anderson and Walmsley (1964) at 77 K and later by Ron and Schnepp (1967) at 20°K. Recently, helium temperature measurements were carried out by Kuan (1969) and 35°K measurements by Brown and King (1970). Of these workers, only Kuan prepared the solid sample from the vapor under equilibrium conditions. The results show that the frequencies of the two infrared active modes are not very sensitive to temperature or to sample preparation. On the other hand, the line widths observed by Kuan are about half those reported by Brown and King. Kuan s line widths are given in Table V. Moreover, the measured intensity ratios differ markedly (both values are listed in the table). 

For comparison, the Sun s absorption spectrum is also shown Figure 2.41. Because the Sun is at the lower temperature, different particles are able to absorb visible light. For example, lines from sodium, iron and magnesium can be seen. The Sun s chromosphere consists mainly of hydrogen and helium but, at the temperature of the Sun, these do not absorb visible light. 

In liquid helium ( He), the electron trap is thought to consist of a spherical void in the liquid of about 2-nm radius (see Section 7.2). Grimes and Adams (1990) produced electrons in liquid helium by field emission from tungsten tips and measured their optical absorption. The absorption spectrum is shown in Figure 33. 

One of the first applications of RQMC was to the rotational dynamics of carbonyl sulfide (OCS) molecules solvated in helium clusters, for cluster sizes (tV = 3,10) [42]. This and related work, described shortly, rest on the absorption spectrum given by the Fourier transform of the reptilian imaginary time electric dipole correlation function. Similarly, the optical activity is extracted from the autocorrelation of the molecular orientation vector. This work by Moroni and coworkers and/or Boroini and co-workers was closely followed by several other investigations of rotational dynamics in doped clusters, summarized as follows ... 

At liquid helium temperature, the absorption spectrum of pentacene at each site reveals an intense zero-phonon line associated with the electronic transition (Figure 7.14) and an accompanying phonon sideband (not shown in Figure 7.14). The latter appears as a mirror image in fluorescence and excitation and stems from pseudo-local phonons due to guest-host interactions [155]. The B2U pentacene transition in p-terphenyl is strongly b-axis polarized [250,251]. 

Propose an absorption spectrum of a helium atom that is initially in the ground-state. Label each absorption line with the transition using term symbols. 

The molecular constants that describe the stnicture of a molecule can be measured using many optical teclmiques described in section A3.5.1 as long as the resolution is sufficient to separate the rovibrational states [110. 111 and 112]. Absorption spectroscopy is difficult with ions in the gas phase, hence many ion species have been first studied by matrix isolation methods [113], in which the IR spectrum is observed for ions trapped witliin a frozen noble gas on a liquid-helium cooled surface. The measured frequencies may be shifted as much as 1 % from gas phase values because of the weak interaction witli the matrix. 

Solid covalent dinitrogen pentoxide can be prepared by freezing the vapour with liquid helium. Normally, solid dinitrogen pentoxide exists as (NO2+) (NOj ), showing absorption bands in its Raman spectrum only at 1050 and 1400 cm the structure of this form has been determined by X-ray crystallography. ... 

Fig. 2.4. The asymptotic behaviour of the IR spectrum beyond the edge of the absorption branch for CO2 dissolved in different gases (o) xenon (O) argon ( ) nitrogen ( ) neon (V) helium. The points are experimental data, the curves were calculated in [105] according to the quantum J-diffusion model and two vertical broken lines determine the region in which Eq. (2.58) is valid.

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 PAS phenomenon involves the selective absorption of modulated IR radiation by the sample. The selectively absorbed frequencies of IR radiation correspond to the fundamental vibrational frequencies of the sample of interest. Once absorbed, the IR radiation is converted to heat and subsequently escapes from the solid sample and heats a boundary layer of gas. Typically, this conversion from modulated IR radiation to heat involves a small temperature increase at the sample surface ( 10 6oC). Since the sample is placed into a closed cavity cell that is filled with a coupling gas (usually helium), the increase in temperature produces pressure changes in the surrounding gas (sound waves). Since the IR radiation is modulated, the pressure changes in the coupling gas occur at the frequency of the modulated light, and so does the acoustic wave. This acoustical wave is detected by a very sensitive microphone, and the subsequent electrical signal is Fourier processed and a spectrum produced. 

The second source for which it has been claimed the detection of redshifted spectral lines is IE 1207.4-5209, a radio-quite compact star located in the center of the supernova remnant PSK 1209-51/52. IE 1207.4-5209 has been observed by the Chandra X-ray observatory. Two absorption features have been detected in the source spectrum and have been interpreted (Sanwal et al. 2002) as spectral lines associated with atomic transitions of once-ionized helium in the atmosphere of a strong magnetized (B 1.5 x 1014 G) compact star. This interpretation gives for the gravitational redshift at the star surface z = 0.12 -0.23 (Sanwal et al. 2002), which is reported in Fig. 3 and by the two dashed lines labeled z = 0.12 and z = 0.23. 

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