Partially resolved rotational structure in the photoacoustic spectrum of I2

Abstract

We reported recently1 a partially resolved rotational structure representing the [(14,2), (12,1)] and [(13,2), (11,1)] bands in the photoacoustic spectrum of I2 due to X 1 Σ g + − B 3 I I ( 0 u + ) transition. We now report a similar structure in the 16,900–17,000-cm–1 region representing the [(13,1),(15,2)] bands. The spectrum is recorded with the photoacoustic spectrometer reported earlier.2 A comparison of the photoacoustic spectrum with the absorption spectrum in the I2 atlas of Gerstenkor and Luc helped in its analysis. Vibrational-rotational energy transfers in the B and X states are probably responsible for the photoacoustic spectrum. The rotational lines [P(57), R(52)] of the band (13,1) and [P(49), R(54)] of (15,2) expected around 16,962.4 cm–1 and a similar group expected around 16,911.5 cm–1 are nearly extinct. This suggests that molecules reaching the corresponding upper levels do not transfer their energy to the medium. Possible mechanisms such as multiphoton ionization and fluorescence to υ″ = 0 from these levels are discussed to understand this observation.