Description of the absorption spectrum of bromine recorded by means of Fourier transform spectroscopy : the (B 3Π0+ u ← X 1 Σ+g) system

Abstract

2014 L'analyse du spectre d'absorption de la molécule de brome représenté par le système (B-X ) Br2 et enregistré par spectroscopie par Transformée de Fourier est présentée. On montre que les 80 000 transitions enregistrées couvrant le domaine 11600-19 577 cm-1 et publiées sous forme d'un atlas peuvent être recalculées au moyen de 39 constantes : 38 étant les coefficients de Dunham servant à décrire les constantes vibrationnelles et rotationnelles des états X jusqu'à 03BD" = 14 et de l'état B jusqu'à v' = 52 (niveau situé à 5,3 cm-1 de la limite de dissociation) plus un coefficient empirique permettant de tenir compte des constantes de distorsions négligées (supérieures à M03BD). L'erreur quadratique moyenne entre les nombres d'ondes recalculés et mesurés est trouvée égale à 0,0016 cm-1 en accord avec l'incertitude estimée des mesures expérimentales.Abstract. 2014 An in extenso analysis of the (B-X ) Br2 bromine absorption spectrum recorded by means of Fourier Transform Spectroscopy is presented. It is shown that the 80 000 recorded transitions covering the 11600-19 577 cm-1 range and published in an atlas form may be recalculated by means of only 39 constants : 38 are Dunham coefficients describing the vibrational and rotational constants of both X state (up to 03BD" = 14) and B state (up to 03BD' = 52, situated only at 5.3 cm-1 from the dissociation limit of the B state), and one empirical scaling factor which takes account of neglected centrifugal constants higher than M03BD. The overall standard error between computed and measured wavenumbers is equal to 0.0016 cm-1 in agreement with the experimental uncertainties.

Characterization of the Ground State of Br2 by Laser-Induced Fluorescence Fourier Transform Spectroscopy of the B3Π0+u–X1Σ+g System

“…The fluorescence spectrum of the (19,22). It should be noted that the Br 2 fluorescence spectra were strictly resonant, i.e., no rotational or vibrational relaxation has been observed in the upper state.…”

“…(42)(43)(44)(45)(46)(47)(48)). At this stage of the work, the very good rovibrational constants derived by Gerstenkorn et al (22) from their absorption study of the B 3 ⌸ 0 ϩ u -X 1 ⌺ g ϩ system of Br 2 were of great help. The DSParFit program is able (among other features) to fit directly the fluorescence series while varying only the lower state spectroscopic constants and the energies of the various excited state levels.…”

“…to aid in the assignments. This program used the constants of both upper and lower states (22) in order to find a match between the experimental line positions and the calculated ones. The results obtained by the two programs were the same, giving us a positive test for the validity of our assignments.…”

“…Several of these progressions were excited twice (by very close positions of the laser line), so only 85 of them are distinct. A listing of these 85 fluorescence excitation transitions is given in Table 1, together with the range (v Љ min , v Љ max ) of the ground state vibrational levels observed, the assignment (vЈ, JЈ) 4 (vЉ, JЉ) of the line excited by the laser and its position calculated from the Gerstenkorn et al (22) constants. The Gerstenkorn et al (22) constants describe very well the vЉ ϭ 0-14 and the vЈ ϭ 0-48 regions of the potential curves of the X 1 ⌺ g ϩ and B 3 ⌸ 0 ϩ u states, respectively, and, as one can see from Table 1, our excitation lines involved only the vibrational levels vЉ ϭ 0-3 and vЈ ϭ 10-22.…”

“…In 1971, Coxon (17) (22) provides the most reliable high-resolution data for the B 3 ⌸ 0 ϩ u -X 1 ⌺ g ϩ system of Br 2 and their constants will be used extensively in the present work. Our work will focus on the X 1 ⌺ g ϩ ground state and spectroscopic information concerning this state could also be derived from the A 3 ⌸ 1u -X 1 ⌺ g ϩ extreme red system (9,14,16,(25)(26)(27)(28).…”