Balmer spectra

Not much is known about these processes, but they must be included to give a total picture. Emissions of Lyman and Balmer spectra of the H atom upon e-impact on hydrocarbons, H2, and H20, discussed in Sect. 4.3.2, fall in this category. Similarly, many of the excited states observed in dissociated radicals via electron impact on stable molecules (Polak and Slovetsky, 1976) also belong to this category. It is known from the dipole oscillator spectrum of H20 (Platzman, 1967) that most ionizations are accompanied by considerable excitation. Excitation transfer to the neighboring neutral molecule followed by fast dissociation cannot be ruled out. 

The Balmer Spectrum of Hydrogen An Old Experiment with a New Twist 154... 

Mass Ratio of the Deuteron and Proton from the Balmer Spectrum of Hydrogen 157... 

Historically, the simple and regular Balmer spectrum has inspired. ... 

Starting somewhat later, Dirac applied his version of the new quantum mechanics to the hydrogen atom. Dirac s approach to the hydrogen atom was very different and more general than PauH s method and it too was successful in explaining the Balmer spectrum of the hydrogen atom. Dirac s paper on the hydrogen... 

Optical spectroscopy of the simple hydrogen atom has played a central role in the development of atomic physics and quantum mechanics.3 The visible Balmer spectrum was the Rosetta stone which inspired the pathbreaking discoveries of Bohr, Sommerfeld, De Broglie, Schrbdinger, Dirac, and Lamb. More than once, seemingly minute discrepancies between theory and experiment led to important breakthroughs in our understanding of quantum physics. 

Fig. 2 Top Balmer spectrum of atomic hydrogen. Center Doppler profile of the Balmer-a line at room temperature and theoretical fine structure components. Bottom Doppler-free spectrum of Balmer-a, recorded by saturated absorption spectroscopy with a pulsed dye laser.

Bafmer series Frequencies of certain lines in the spectrum of hydrogen are simply related to each other, and can be expressed by a general formula. One group of lines is termed the Balmer series. Other series were later discovered in the spectrum of hydrogen by Lyman, Paschen, Brackett and Pfund. 

Whereas the emission spectrum of the hydrogen atom shows only one series, the Balmer series (see Figure 1.1), in the visible region the alkali metals show at least three. The spectra can be excited in a discharge lamp containing a sample of the appropriate metal. One series was called the principal series because it could also be observed in absorption through a column of the vapour. The other two were called sharp and diffuse because of their general appearance. A part of a fourth series, called the fundamental series, can sometimes be observed. 

Historically, the visible emission lines shown in Figure 15-3 were the first atomic hydrogen lines discovered. They were found in the spectrum of the sun by W. H. Wollaston in 1802. In 1862, A. J. Angstrom announced that there must be hydrogen in the solar atmosphere. These lines were detected first because of the lesser experimental difficulties in the visible spectral region. They are called the "Balmer series because J. J. Balmer was able to formulate a simple mathematical relation among the frequencies (in It S). The ultraviolet series shown in Figure 15-3 was... 

The first person to identify a pattern in the lines of the visible region of the spectrum was Joseph Balmer, a Swiss schoolteacher. In 1885, he noticed that the frequencies of all the lines then known could be generated by the expression... 

This wavelength, 657 nm, corresponds to the red line in the Balmer series of lines in the spectrum. 

Balmer series A family of spectral lines (some of which lie in the visible region) in the spectrum of atomic hydrogen. 

Local thermal equilibrium (LTE) is an assumption that allows for the molecules to be in equilibrium with at least a limited region of space and remains an assumption when using the Boltzmann law for the relative populations of energy levels. The LTE assumption notwithstanding, observation of a series of transitions in the spectrum and measurement of their relative intensities allows the local temperature to be determined. We shall see an example of this in Section 4.4 where the Balmer temperature of a star is derived from the populations of different levels in the Balmer series. 

There are in principle an infinite number of series beginning at higher quantum numbers with i = 6, 7, 8, 9... but they become increasingly difficult to observe. For the higher n series to be seen in the spectrum the levels have to be populated, so some hydrogen atoms must be in the n = 5 level to see the Pfund series. We shall see that the presence of the Balmer series in the spectrum of a star is indicative of the stellar temperature, which is a direct consequence of the population of the energy levels. More of this in Chapter 4. 

The Balmer series is seen in many but not all stars because the first energy level in the series is an excited state with quantum number n = 2. There has to be a mechanism by which the excited stated is populated and this is the local temperature of the star. Hence only if the star is sufficiently hot will the spectrum contain the Balmer series. The strength of the Balmer series within the stellar spectrum can be used to derive a temperature for the surface of the star to compare with black body temperature and the B/V ratio. 

This is a similar value to the temperature of the Sun derived optically or from A.max in the black body spectrum. In a colder star the Balmer series is weaker still, but in a hotter star the Balmer series lines are stronger. In very hot stars the Balmer series may become weaker again due to collisional ionisation of H atoms, removing the electrons from the atoms completely. 

Balmer series The series in the spectrum of atomic hydrogen with lower level n = 2 and all other possible levels n = 3,4,5,... 

The frequencies of hydrogen emission lines in the infrared region of the spectrum other than the visible region would be predicted by replacing the constant 2 in the Balmer equation by the variable m, where m is an integer smaller than n m = 3,4,... 

Figure 2.1 Electronic orbitals and the resulting emission spectrum in the hydrogen atom, (a) Bohr orbitals of the hydrogen atom and the resulting spectral series, (b) emission spectrum of atomic hydrogen. The spectrum in (b) is calibrated in terms of wavenumber (P), which is reciprocal wavelength. The Balmer series, which consists of those transitions terminating on the second orbital, give rise to emission lines in the visible region of the spectrum. ( 1990 John Wiley Sons, Inc. Reprinted from Brady, 1990, by permission of the publisher.)...

Figure 12.6 The emission spectrum of hydrogen in the UY, visible and near infrared, showing the families of lines labeled Lyman (n = 1), Balmer (n — 2), and Paschen (n = 3).

Balmer jump spect The sudden decrease in the intensity of the continuous spectrum of hydrogen at the Balmer limit. Also known as Balmer discontinuity, bob mor ijamp )... 

Balmer lines spect Lines in the hydrogen spectrum, produced by transitions between = 2 and > 2 levels either in emission or in absorption here is the principal quantum number. bobmor, lTnz ... 

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