Photofragment translational spectroscopy at 304 nm from C-H symmetric stretch excited CH3I [v 1 = 1]

The 304 nm photodissociation of the C-H symmetric stretch excited CH₃I v ₁ = 1, v ₂ = 0] (v ₁ denotes the C-H symmetric stretch mode, and v ₂ denotes the umbrella mode) is studied with our simple photofragment translational spectrometer. An IR laser is used to excite the ground state CH₃I 0, 0] to the C-H symmetric stretch excited CH₃I 1, 0]. With IR laser OFF and ON, the fractions of photofragments CH₃ (ν ₁, ν ₂) from the 304 nm photodissociation of CH₃I 1, 0] have been determined through the photofragment translational spectra (PTS) from measuring I and I* and also through the PTS from measuring CH₃ (0, 0) (1, 0) (0, 1) and (1, 1). The experimental results show that the C-H symmetric stretch vibration (v ₁ = 1) in parent molecules is about 66% retained in the photofragments in the I channel, but only 24% in the I* channel. The populations of photofragments CH₃ (0, 2) and (0, 3) are higher than CH₃ (0, 0) and (0, 1), showing strong inverted population both in I and I* channels.