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 $X^1{\Sigma }_g^{+}-B^{3}II\left(0_u^{+}\right)$ 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.

© 1989 Optical Society of America