Magnesium spectral features

Fig. 3.17. Spectrum of the central region of an SO galaxy, NGC 3384, showing hydrogen, magnesium and iron spectral features used in the Lick system. The resolution is 3.1 A ( 75kms 1), compared to a line-of-sight velocity dispersion 140kms 1. After Fisher, Franx and Illingworth (1996). Courtesy Garth Illingworth.

In a 1- or 1.5-litre round-bottomed flask prepare a solution of 53.5 g (0.5 mol) of o-toluidine in 170 ml of 40 per cent w/w hydrobromic acid cool to 5 °C by immersion in a bath of ice and salt. Diazotise by the gradual addition of a solution of 36.5 g (0.53 mol) of sodium nitrite in 50 ml of water stopper the flask after each addition and shake until all red fumes are absorbed. Keep the temperature between 5 and 10 °C. When the diazotisation is complete, add 2g of copper powder or copper bronze (Section 4.2.79, p. 426), attach a reflux condenser to the flask and heat very cautiously on a water bath. Immediately evolution of gas occurs, cool the flask in crushed ice unless the flask is rapidly removed from the water bath, the reaction may become so violent that the contents may be shot out of the flask. When the vigorous evolution of nitrogen moderates, heat the flask on a water bath for 30 minutes. Then dilute with 400 ml of water, and steam distil the mixture until about 750 ml of distillate are collected. Render the distillate alkaline with 10 per cent sodium hydroxide solution (about 50 ml) and separate the lower red layer of crude o-bromotoluene. Wash it with two 20 ml portions of concentrated sulphuric acid (which removes most of the colour) and then twice with water. Dry with magnesium sulphate or anhydrous calcium chloride, and distil from a flask fitted with a lagged fractionating column. Collect the o-bromotoluene at 178— 181 °C. The yield is 40 g (47%). The spectral features are noted in Expts 6.72 and 6.81. 

Generally, the calculated spectra reproduce the general qualitative features of the experimental spectra quite well. The visible bands of magnesium and free-base porphine are predicted to arise from weakly-allowed transitions to a doubly-degenerate (n, tt ) state and a pair of (tt, n ) states, respectively, a picture basically similar to the 4-orbital model. In the Soret spectral region, however, the present studies reveal that this band is composed of a number of intense tt tt transitions, a result which represents a fundamental departure from the basic 4-orbital model [13]. The results further suggest that resolution of the Soret spectral region into individual electronic transitions would be difficult experimentally, and perhaps is best achieved currently with a computational approach. 

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