Photoacoustic spectrum (17,750-18,960 cm–1) of Br2

Abstract

Kumar et al. 1 recorded the photoacoustic spectrum (16,100-17,400 cm–1) of Br2 using a flashlamp pumped dye laser. We recorded here the spectrum in the 17,840–18,900-cm–1 region using an excimer laser pumped tunable dye laser and a photoacoustic spectrometer recently assembled.2 Optogalvanic spectrum of Ne is used for wavelength standards. Partial pressure of Br2 is ~250 Torr and that of air is 510 Torr. This spectrum involves the transition X 1 Σ g + → B 3 I I ( 0 u + ) with (18 ≤ V ≤ 49) and (0 ≤ V" ≤ 5). Nonradiative vibrational-rotational energy transfers in B and X states are responsible for the photoacoustic spectrum. High values of υ" are reached by fluorescence from the B state and they go to lower levels only by nonradiative energy transfers as Br2 is homonuclear. The result is that V" = 4 and 5 are well populated at room temperature although the corresponding Boltz-mann factor for these levels is not high.