The photodissociation dynamics of propyl iodides n-C3H7I and i-C3H7I near 280 and 304 nm has been investigated with our mini-TOF photofragment translational spectrometer. When a single laser is applied for both the photodissociation of parent molecules and the REMPI of I atom photofragments, the TOF spectra of photofragments I*(2P1/2) and I (2P3/2) are obtained at four different wavelengths for these two iodides. For n-C3H7I, some small vibrational peaks are partially resolved (with separation of approximately 522 cm-1, corresponding to the RCH2 deformation frequency of the fragment n-C3H7) at 281.73, 279.71, and 304.67 nm. These results show that the RCH2 deformation is mostly excited. For i-C3H7I, we obtain some partially resolved vibrational peaks (with separation of approximately 352 cm-1, corresponding to the HC(CH3)2 out-of-plane bending frequency of the fragment i-C3H7) at 281.73 nm only. For n-C3H7I, the partitioning values of the available energy Eint/Eavl are 0.48 at 281.73 nm and 0.49 at 304.02 nm for the I* channel, and 0.52 at both 279.71 and 304.67 nm for the I channel. These energy partitioning values are comparable with the previous results at different wavelengths in the literature. For i-C3H7I, the Eint/Eavl values are 0.61 at 281.73 nm, 0.65 at 304.02 nm for the I* channel, and 0.62 at 279.71 nm, 0.49 at 304.67 nm for the I channel. The potential-energy-surface crossing and the beta values have also been discussed.
The photodissociation of ethyl iodide at 279.71, 281.73, 304.02 and 304.67 nm has been studied on our new mini-photofragment translational spectrometer with a total flight path of only 5 cm. Some vibrational peaks are firstly resolved in the TOF spectra of I*( 2 P 1/2 ) and I( 2 P 3/2 ) channels. These vibrational peaks are assigned to the excitation states (ν 2 = 0, 1, 2,…) of the umbrella mode (ν 2 , 540 cm −1 ) of the photofragment C 2 H 5 , and the distribution of the vibrational states is obtained. The dissociation energy has been determined to be D 0 (C-I)=2.314 ± 0.03 eV. The energy partitioning of the available energy (E avl =E T +E int =E T +E V,R ) calculated from our experimental data / int avl E E = 22.1% at 281.73 nm, 22.4% at 304.02 nm for the I* channel, and / int avl E E = 25.2% at 279.71 nm, 25.9% at 304.67 nm for the I channel, seem to be more reliable. photofragment translational spectroscopy, C 2 H 5 I, photodissociation, vibrational state distribution, energy partitioning,dissociation energyFor the photodissociation of molecules, photofragment translational spectroscopy offers a way to study the dynamics of photodissociation in a collision-free regime [1] . Analysis of the velocity distribution and the angular distribution of the photofragments can give information of the potential energy surfaces, the energy partitioning, the vibrational state distribution of the photofragments, the dissociation energy, the life time of the excitation state and the curve-crossing. The original photofragment translational spectrometer (PTS) [2,3] was with the structure that the molecular beam, the laser, and the detection axis were perpendicular to each other. The improved PTS, with the molecular beam rotatable, was called the "Rotating Source Machine" at Yuan Lee's Lab in U.C. Berkeley [4] . At the same time, similar experimental set-ups were built in the University of Manchester [5] and in our laboratory [6,7] . This kind of experimental apparatus is still used in many laboratories. Some high resolution experimental results have been obtained [8,9] , but the apparatus is very complicated and in need of ultra-high vacuum up to 10 −8 Pa. At present, the ion imaging apparatus, originally designed by Chandler and Houston [10] , and improved by Eppink and Parker [11] , is used more often. From the ion image, the angular distribution of the photofragments can be obtained simultaneously with the high-resolution velocity distribution, but high-grade uniform Micro Channel Plates (MCP) and CCD camera are required. We have built a simple and small photofragment translational spectrometer of only 5 cm total flight path and used a simple MCP as the detector. However, the resolution of this PTS is high enough to resolve some vibrational states of the photofragments.Alkyl halides have been concerned to the atmospheric chemistry due to their role in ozone depletion. The photodissociation of ethyl iodide (C 2 H 5 I) has been widely studied [12][13][14][15][16][17][18][19] . The absorption cross-section of C 2 H 5 I was meas...
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