• P Ramakoteswara Rao

Articles written in Proceedings – Section A

• The near ultra-violet emission spectrum of phenetole

A band system has been recorded in the 2750–3400 Å region in the spectrum of an uncondensed transformer discharge through the flowing vapour of phenetole (C6H5OC2H5). This system is found to correspond to the known absorption band system of phenetole molecule in the near ultra-violet region. Vibrational analysis of the system is discussed.

• Spectroscopic studies of the cresols - I. Emission and absorption spectra ofPara-cresol in the near ultra-violet region

After giving a brief summary of the earlier spectroscopic work on the cresols, the paper deals with the emission spectrum of para-cresol in Part A and its absorption spectrum in Part B.

Part A.—The emission spectrum of para-cresol, obtained by means of a transformer discharge through its flowing vapour, was recorded on the Hilger medium quartz (E2) spectrograph. The spectrum consists of nineteen bands in the region 2810–3090 Å superposed on a continuum extending in the region 2830–3300 Å. The discrete emission spectrum is the counterpart of the near ultra-violet absorption spectrum of para-cresol (Part B). The electronic transition involved in the discrete band system is interpreted as1B1-1A1. A vibrational analysis of the system is proposed in terms of the ground state vibrational frequencies 231, 464, 846 and 1267 cm.−1 and the excited state frequency 217 cm.−1

Part B.—The absorption spectrum of para-cresol vapour, using absorption paths ranging from 20 to 100 cm. and temperature 0 to 30° C., is recorded on the Hilger large quartz (E1) spectrograph. About sixty-five bands are obtained in the region 2560–2910 Å. A vibrational scheme is proposed for the bands in terms of the excited state vibrational frequencies 217, 420, 806, 1194 and 1273 cm.−1 and the ground state frequencies 231, 464 and 846 cm.−1 The vibrational analysis presented in this paper is compared with those proposed by earlier investigators.

• Spectroscopic studies of the cresols - II. Emission and absorption spectra of ortho-cresol in the near ultra-violet region

Part A

The emission spectrum of ortho-cresol, obtained by means of a controlled transformer discharge through the flowing vapour of the substance, is photographed on the Hilger medium (E2) quartz spectrograph. The spectrum consists of twenty-seven bands in the region 2690–2950 Å superposed over a continuum beginning at about 2780 Å and extending to beyond 3200 Å. The discrete emission spectrum is the counterpart of the near ultra-violet absorption spectrum of ortho-cresol (Part B). The electronic transition involved in the discrete band system is interpreted as1A′-1A′ with the band at 36420 cm.−1 as the zero-zero band. A vibrational analysis of the band system is proposed in terms of the ground state vibrational frequencies 192, 278, 524, 590, 744, 1040, 1163 and 1261 cm.−1 and the excited state frequencies 124, 202 and 702 cm.−1

Part B

The absorption spectrum of ortho-cresol vapour, obtained by using cells of lengths 20, 50, 150 and 250 cm. in the temperature range 0° C. to 30° C., is photographed on the Hilger large quartz (E1) spectrograph. About seventy bands are obtained in the region 2560–2790 Å. A vibrational analysis of the system is proposed in terms of the excited state vibrational frequencies 124, 202, 360, 702, 719, 944, 955 and 1251 cm.−1 and the ground state frequency 278 cm.−1

• Spectroscopic studies of the cresols - III. Emission and absorption spectra of meta-cresol in the near ultra-violet region

Part A:—The emission spectrum of meta-cresol, obtained by means of a controlled transformer discharge through the flowing vapour, is recorded on the Hilger medium quartz (E2) spectrograph. The emission spectrum consists of fifteen bands in the region 2750–2920 Å superposed over a continuum beginning at about 2770 Å and extending to beyond 3100 Å. The discrete emission spectrum is the counterpart of the near ultra-violet absorption spectrum of meta-cresol vapour (Part B). The electronic transition involved in the discrete band system is interpreted as1A′ –1A′. A vibrational analysis of the band system is proposed in terms of the ground state vibrational frequencies 200, 401, 735 and 1003 cm.−1 and the excited state frequencies 116, 188 and 251 cm.−1

Part B:—The absorption spectrum of meta-cresol vapour, using absorption paths ranging from 100–250 cm. and temperatures from 0–30°C., is recorded on the Hilger large quartz (E1) spectrograph. About fifty-five bands are obtained in the region 2580–2810 Å. A vibrational scheme for the band system is proposed in terms of the excited state vibrational frequencies 116, 188, 251, 469, 696, 964 and 1031 cm.−1 and the ground state frequencies 200, 248 and 401 cm.−1

• Isotope shifts in the uranium spectrum

Isotope shifts in over twenty lines of the UI spectrum excited in a hollow cathode discharge, in the region 5200 to 6000 Å, have been recorded on a Fabry-Perot spectrometer equipped with a photoelectric detector and the results are used to check the line classification.

• A new band system of CuBr molecule

A new system of red degraded bands in the 3700–4000 Å region has been obtained in the spectrum of the CuBr molecule excited in an electrodeless discharge tube by a microwave oscillator. The band heads of this system are given by the formula:$$\begin{gathered} v ^{63} Cu ^{79} Br = 25538 \cdot 5 + 281 \cdot 9 \left( {\upsilon ' + \tfrac{1}{2}} \right) - 1 \cdot 35 \left( {\upsilon ' + \tfrac{1}{2}} \right)^2 - 314 \cdot 4 \hfill \\ \left( {\upsilon '' + \tfrac{1}{2}} \right) + 0 \cdot 86 \left( {\upsilon '' + \tfrac{1}{2}} \right)^2 \hfill \\ \end{gathered}$$. It has been found that the lower electronic state of this system is the same as the common lower state of the three known band systems, which is also the ground state of the molecule.

Some new bands recorded in the B and C systems are assigned vibrational quantum numbers.

• Electrodeless discharge lamps and some features of spectra emitted by them

Some salient features, such as self-absorption and selective excitation of elements, of microwave excited thorium iodide and other electrodeless discharge lamps are discussed. The importance of these features for classification and analysis of spectra and possibly for spectrochemical analysis is indicated. The use of the electrodeless lamp as a source for the excitation of molecular spectra is pointed out.

• Isotope shifts in the second negative bands of O2+

The second negative bands of O2+, lying in the region 5000–1850 Å, have been photographed using oxygen enriched in18O. A study of the isotope shifts in the band heads revealed that thev″ numbering is to be increased by one unit whereas thev′ numbering remains unaltered. This change in vibrational numbering leads to a revision of the molecular constants of O2+, especially of those in its ground state. These are discussed and the extension of the band system in the vacuum ultra-violet region reported. The possibility of developing a simple spectrographic method for the isotopic assay of oxygen using the isotope shifts in this band system is pointed out. The revised rotational and vibrational constants in theX2IIg ground state of O2+ molecule are as follows :$$\begin{gathered} \omega _e = 1903 \cdot 85 cm.^{ - 1} , \hfill \\ \omega _e x_e = 16 \cdot 18 cm.^{ - 1} , \hfill \\ B_e = 1 \cdot 6920 cm.^{ - 1} \hfill \\ and \hfill \\ r_e = 1 \cdot 1161 {\AA}. \hfill \\ \end{gathered}$$.

• Absorption and fluorescence spectra of praseodymium in KCl and KBr matrices

The observed fluorescence and absorption spectra of single crystals of KCl and KBr doped with praseodymium (Pr) show that the rare earth enters substitutionally as Pr3+ in these lattices. However, the site symmetry of the ion has at most a twofold axis. This is shown by the fact that thej-degeneracy of its energy levels is completely removed. Fluorescence is observed to occur only from3P0 level to3F2, 3, 4 and3H6 levels. The overall Stark splitting shows that the Pr3+ ion experiences a stronger field in these matrices than in LaCl3 or LaBr3.

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