## Abstract

A new emission band spectrum has been observed in the iodine-fluorine flame of reaction and has been assigned to the IF molecule. A similar type of spectrum is emitted by the bromine-fluorine flame and is shown to be an extension of the BrF system already known in absorption. Both these systems probably arise from a $^{3}\Pi _{0}$+$\rightarrow $$^{1}\Sigma $ transition. Vibrational analyses of the two spectra give the following constants: $ \matrix\format\l\kern.8em&\l\kern.8em&\l\kern.8em&\l \\ \text{IF} & \ \nu _{e}=19054\,\text{cm}.^{-1} & \omega _{e}^{\prime}=412.5 & \,x_{e}^{\prime}\omega _{e}^{\prime}=3\cdot 8 \\ & \nu _{00}=18955\,\text{cm}.^{-1} & \omega _{e}^{\prime \prime}=610 & x_{e}^{\prime \prime}\omega _{e}^{\prime \prime}=3 \\ \text{BrF} & \ \nu _{e}=18650\,\text{cm}.^{-1} & \omega _{e}^{\prime}=365 & x_{e}^{\prime}\omega _{e}^{\prime}=6 \\ & \nu _{00}=18495\,\text{cm}.^{-1} & \omega _{e}^{\prime \prime}=673 & \,x_{e}^{\prime \prime}\omega _{e}^{\prime \prime}=4 \endmatrix $ A Birge-Sponer extrapolation for the upper state of IF gives D$_{0}^{^{\prime \prime}}$(IF) = 1$\cdot $98 or 2$\cdot $87 $\pm $ 0$\cdot $04 eV, depending on whether the upper state dissociates to excited I and normal F or vice versa. Available evidence favours the lower value for D$_{0}^{\prime \prime}$(IF) (=1$\cdot $98 $\pm $ 0$\cdot $04 eV), i.e. upper state dissociates to excited I and normal F. By analogy, if we assume the upper state of BrF dissociates to excited Br and normal F, a Birge-Sponer extrapolation gives D$_{0}^{\prime \prime}$(BrF) = 2$\cdot $16 $\pm $ 0$\cdot $02 eV.

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