Ultraviolet photodissociation of C2F5I with a small and simple photofragment translational spectrometer

Abstract

Photodissociation dynamics of C(2)F(5)I near 280 and 304 nm has been investigated on a small and simple time-of-flight photofragment translational spectrometer (PTS). On this new PTS, the photolyzed and ionized fragments, not accelerated by electric field, travel freely for a short flight path (<50 mm) and are detected by microchannel plates. In the spectra of the I(*)((2)P(1/2)) channel at 281.73 and 304.02 nm, vibrational peaks with spacing of approximately 350 cm(-1) are partially resolved, indicating the preferential excitation of CF(2) wag mode (nu(11)=366 cm(-1)) of C(2)F(5) photofragment. The fraction of the available energy disposed into the internal energy is higher than 50% for both I(*) channel and I channel, showing the high excitation of vibration in the C(2)F(5) fragments. The fragment recoil anisotropy parameter beta(I(*)), determined to be 1.70 at 281.73 nm and 1.64 at 304.02 nm, reveals that I(*) atoms are produced predominantly from the parallel (3)Q(0) <-- N transition. The anisotropy parameter beta(I), determined to be 1.25 at 279.71 nm and 0.88 at 304.67 nm, implies that I atoms are produced from two excited states, i.e., direct dissociation via the perpendicular (3)Q(1) <-- N transition, and indirect dissociation via the parallel (3)Q(0) <-- N transition then curve crossing to the (1)Q(1) potential energy surface. Analysis on the recent studies with vibrational state resolution in the photodissociation of alkyl iodides in the A band reveals that the "symmetric bending" mode on alpha-carbon of alkyl iodides is the preferential vibrational excitation mode, which can be explained by the classic impulsive model.