Mercury line spectrum

One of the lines in the line spectrum of mercury has a wavelength of 435.8 nm. (a) What is the frequency of this line (b) What is the wave number for the radiation (c) What energy (in kj mol-1) is associated with this radiation ... 

Soon after Dennison had deduced from the specific-heat curve that ordinary hydrogen gas consists of a mixture of two types of molecule, the so-called ortho and para hydrogen, a similar state of affairs in the case of iodine gas was demonstrated by direct experiment by R. W. Wood and F. W. Loomis.1 In brief, these experimenters found that the iodine bands observed in fluorescence stimulated by white light differ from those in the fluorescence excited by the green mercury line X 5461, which happens to coincide with one of the iodine absorption lines. Half of the lines are missing in the latter case, only those being present which are due to transitions in which the rotational quantum number of the upper state is an even integer. In other words, in the fluorescence spectrum excited by X 5461 only those lines appear which are due to what we may provisionally call the ortho type of iodine molecule. 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

Also important, besides the variables of the equation, are temperature of the solution, wavelength of the light source, and concentration of the solution. The standard light source used to measure optical rotation has been the bright yellow D lines of the sodium spectrum, but the single mercury line, X = 5461 A, is now used frequently for precision measurements. Generally, the specific rotation is reported at 20 °C and expressed as ... 

These lamps are short-arc mercury lamps containing a metal halide surrounded by a glass envelope. The metal used is generally one with a very rich line spectrum, low ionization potential, and low corrosivity. They are available as both air- and water-cooled varieties. 

It should also be noted that the spectral power distribution for the "cool white" lamp given in ISO 10977 1993(E) is not that of "cool white" fluorescent lamp but that of a the visible "cool white" spectrum to which the mercury lines have been added (30). This lamp also has a CCT of approximately 4100 K. There is one known notable exception to this last statement and that is Luzchem Research Inc. (33), which does supply a spectrum for each lamp that they sell if it is to be used for ICH photostability testing. 

Relationship of absorption spectrum to wavelengths of mercury lines. 

Very elegant experiments unequivocally proving the occurrence of electronic energy transfer were performed in 1922 and 1923 by Carlo and Franck [14], When a mixed vapor of mercury and thallium was irradiated with the mercury line at 253.67 nm, the emission lines of thallium could be observed in addition to the anticipated fluorescence spectrum of mercury. Since thallium cannot absorb 253.67-nm light, it must have been sensitized by the excited mercury atoms in order to produce the green fluorescence... 

A tungsten light source does not supply sufficient radiant energy for measurements below 320 nm. In the UV region of the spectrum, a low-pressure mercury-vapor lamp that emits a discontinuous or line spectrum is useful for calibration purposes but is not very practical for absorbance measurements, because it can be used only at certain wavelengths. Hydrogen and deuterium lamps provide sources of continuous spectra in the UV region with some sharp emission... 

Figure 7.7 The line spectra of several elements. A, A sample of gaseous H2 is dissociated into atoms and excited by an electric discharge. The emitted light passes through a slit and a prism, which disperses the light into individual wavelengths. The line spectrum of atomic H is shown (top). B, The continuous spectrum of white light is compared with the line spectra of mercury and strontium. Note that each line spectrum is different from the others.

Mercury or xenon arc lamps are used. A schematic of a xenon arc lamp is given in Fig. 5.42. The quartz envelope is filled with xenon gas, and an electrical discharge through the gas causes excitation and emission of light. This lamp emits a continuum from 200 nm into the IR. The emission spectrum of a xenon arc lamp is shown in Fig. 5.43. Mercury lamps under high pressure can be used to provide a continuum, but low-pressure Hg lamps, which emit a line spectrum, are often used with filter fluorometers. The spectrum of a low-pressure Hg lamp is presented in Fig. 5.44. 

A mercury metal vapor lamp emits a very intense line spectrum. It is possible to use the line spectrum of mercury to excite the fluorescence spectra of elements other than mercury if line overlap exists. Omenetto and Rossi have been able, by this technique, to produce fluorescence spectra of iron, manganese, nickel, chromium, thallium, copper, and magnesium. Table 11-1 illustrates some of these results and also gives detection limits obtained by this method. 

Fluorescent light bulbs often consist of the line spectrum of Hg. Mercury has two strong atomic emission lines in the UV at 254 and 366 nm. (a) Calculate the frequency corresponding with each of these two wavelengths, (b) Calculate the energy of each line in units of joules. 

The further below 260 nm analysis is carried out, the stronger this influence will be. For this reason it is recommended that determination be carried out at the mercury line of 254 nm. The recording of an absorption spectrum can also be used to obtain further information. This method can be supplemented by determining absorption in the visible wavelength range at the mercury line of 436 nm. 

Figure 1 Line spectrum produced from a mercury pen lamp fitted as an alternative source in a high-performance reference commercial spectrophotometer.

Let us summarize the results. The optical spectrum of Hg-N2 close to the P mercury line displays intense structure... 

It had become clearer that the Hght from a glowing soHd body shows a conHnuous spectrum while a metal that is vaporized emits a characterisHc line spectrum. The yeUow doublet in the sodium spectrum was an example. Charles Wheatstone, well known from the science of electricity, in 1835 invesHgated electrical arcs generated between metal electrodes. The metals he used were mercury, zinc, cadmium, Hn, bismuth and lead. He used a prism for studying the radiaHon from the arcs and observed the disHnct Hnes that consHtuted the spectrum. Further he noted that each metal had its special group of Hnes, which could possibly be used for element idenH-ficaHon. 

An early Raman spectrum microphotometer trace (obtained by Raman himself) of diamond is shown in Fig. 2 [7]. It illustrates the difficulty of obtaining such spectra before the invention of the laser and the ready availability of digital computers. Recording was photographic and the Raman frequency was obtained by reference to an iron arc spectrum. The density of the spectral lines on the photographic plate was measured with a microphotometer. Excitation of the Raman spectra was usually accomplished by the 4358-A mercury line from an arc lamp. Unfortunately, this line is not isolated, but accompanied by satellite lines, which mostly could be filtered out or otherwise accounted for (the satellite mercury lines generate satellite Raman bands). Exposure times could be hours. Nevertheless, the measurements were accurate and in no way inferior to many of the results obtained with modem sophisticated instmments. 

The value of the specific rotation depends on the temperature, which is fixed for reference purposes at 20° C. It also depends on the nature of the light source employed. The bright yellow D lines of the sodium spectrum or the yellow-green mercury line, 5461A, are the usual illuminants. The light used is indicated by affixing D or Hg to the symbol denoting the specific rotation. ... 

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