The electronic absorption spectrum of SiF2 has been recorded in the region 2325 to 2130 Å. The principal feature of the spectrum is the presence of a long progression in the bending frequency of the upper electronic state suggesting that the bond angle F–Si–F undergoes a considerable change during transition. A number of weak bands, identified as arising from the vibrationally excited levels of the lower electronic state, are also observed. There is no definite evidence for excitation of stretching vibrations. The bending frequencies for the lower and upper electronic states are estimated as about 345 and 252 cm−1, respectively. The vibrationless transition (ν1′=0, ν2′=0, ν3′=0←ν1″=0, ν2″=0, ν3″=0) is shown to lie at about 2266.4 Å (44 109 cm−1) and is probably a 1B1←1A1 transition.

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The infrared spectrum of gaseous SiF2 has been recorded from 1050 to 400 cm−1. Two bands centered at 872 and 855 cm−1 are, respectively, assigned to the antisymmetric stretching (ν3) and symmetric stretching (ν1) frequencies of the molecule. The symmetric bending frequency (ν2) as determined from the earlier ultraviolet absorption studies lies at 345 cm−1 and could not be observed because this was well below the low-frequency limit of the spectrometer used. The observed vibrational frequencies are combined with the available microwave data to obtain the following values of the quadratic force constants:fr=5.019 mdyn/Å, frr=0.310 mdyn/Å, fα/r2=0.440 mdyn/Å, fαr/r=0.123 mdyn/Å. Two cubic potential constants have been evaluated, K222=−9.5 cm−1 and K122=9.9 cm−1. The average structure of SiF2 in its ground state is computed and found to be 〈r〉=1.5947 Å, 〈α〉=100°53′, where r is the Si–F bond distance and α the F–Si–F angle. A table of thermodynamic functions of SiF2 is presented.

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