Reinvestigation of The Emission Spectra Following the 266 nm Photolysis of Iodomethanes Cian-Ping Tu, Hsin-I Cheng, and Bor-Chen Chang Department of Chemistry National Central University Jhongli 32001, Taiwan CH 2 ICl CH 3 I CH 2 I 2 CHI 3 Emission Spectra Following The 266 nm Photolysis of CHI 3, CH 2 I 2, CH 3 I, and CH 2 ICl I ( 4 P 0 3/2 ) 2 Emission Spectrum Following The Photolysis of CH 2 ICl CH 2 ICl Blank nm (mixed with 532 nm) 266 nm 532 nm Yes No Unknown Bands I 2 at 532 nm Excitation 4 Emission Spectra 5 Unknown Bands I 2 FWHM= 40 cm -1 FWHM= 24 cm -1 6 Unknown Bands I 2 1. Unknown Bands are form by the collisions between iodine atoms generated from the photolysis. 2. Unknown Bands are dominated by the I 2 BX emission. 3. There are more than two upper levels. 4. A least-squares fit still has problems. Vibrational Parameters for the I 2 B 3 + 0,u X 1 + g Transition Emission spectra of the I 2 B-X transition at 9 different excitation wavelengths (509 nm 640 nm) were recorded. A global fit of 385 assigned bands was conducted. (Max. v= 54, Max. v= 45) Standard deviation of the global fit= 4.4 cm -1. 7 Vibrational Parameters (cm -1 ) for I 2 a. G. Herzberg, Molecular Spectra & Molecular Structure. Vol I. b. Gerstenkorn & Luc, J. Physique. 46, 867 (1985). c. Williamson, J. Chem. Educ. 88, 816 (2011). d. One standard deviation in parentheses. 8 Herzberg a Gerstenkorn & Luc b Williamson c This Work d B 3 + 0,u ee (fixed) exeexe (53) eyeeye (23) ezeeze (25) X1+gX1+g ee (3) (fixed) exeexe (22)0.5941(26) eyeeye (4) (64) ezeeze TeTe (6) I 2 B 3 + 0,u X 1 + g (v= 54) Emission at nm Excitation 9 v= v = 33 v= v = 36 Unknown Bands (I 2 B 3 + 0,u X 1 + g v= 33 and 36) 10 266 nm (mixed with 532 nm) 532 nm 266 nm I * ( 4 P 3/2 ) Photolysis of CH 2 I 2 at Different Laser Wavelengths 11 A multiphoton process 12 CH 2 IClCH 2 I 2 CHI nm (mixed 532 nm) YES 516 nm NOYES 532 nm NOYES 610 nm NO Formation of Unknown Bands? Energy is too low! No visible absorption. 13 CH 2 I + I 208 kJ/mol (~ 575 nm) Chen et al., J. Chem. Phys. 134, (2011). Summary Formation of Unknown Bands CH 2 I 2 (CHI 3 ) + h (< 575 nm) CH 2 I + I CH 2 ICl + h (266 nm) CH 2 I + I I + I I 2 I 2 + h (532 nm) I 2 * (B state, v= 33, 36) A global fit of the I 2 BX emission spectra at various excitation wavelengths was conducted for better anharmonicity parameters. $$$ Supports: National Science Council, Taiwan National Central University Many thanks for your attention! 14