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 B→X 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 Π + 0,u −X 1 Σ + 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 Π + 0,u ωe′ωe′ (fixed) ωexe′ωexe′ (53) ωeye′ωeye′ (23) ωeze′ωeze′ (25) X1Σ+gX1Σ+g ωe″ωe″ (3) (fixed) ωexe″ωexe″ (22)0.5941(26) ωeye″ωeye″ (4) (64) ωeze″ωeze″ TeTe (6)

I 2 B 3 Π + 0,u →X 1 Σ + g (v′= 54) Emission at nm Excitation 9

v′′= v′ = 33 v′′= v′ = 36 Unknown Bands (I 2 B 3 Π + 0,u →X 1 Σ + 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 ) + hν (λ< 575 nm) → CH 2 I + I CH 2 ICl + hν (266 nm)→ CH 2 I + I I + I → I 2 I 2 + hν (532 nm)→ I 2 * (B state, v′= 33, 36) A global fit of the I 2 B→X 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