1,4- : 1, 4-,,, PACS: Gj, Lg, Ms, Lp. Acta Phys. Sin. Vol. 61, No. 19 (2012) I( 2 P 3/2 ),

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1 1,4- * 1)2) 1) 1) 1) 1) 1) (, ) 2) (, 5232 ) ( ; ),,., 266 nm I( 2 P 3/2 ), N = , nm, Br ( 2 P 3/2 ) Br ( 2 P 1/2 ), 1, nm Br Br C-Br. β, Br( 2 P 3/2 ) Br ( 2 P 1/2 ).,, 1, 2-, 1, 3-1, nm,. : 1, 4-,,, PACS: Gj, Lg, Ms, Lp 1,,,., [1],,,.,.,,,., [2,3].,., [4 13].,, [14 18]. [14,15], [16,17],., 1, 4-, 1, 4-, * ( : BE ) ( : ) yuzhu.liu@psi.ch c 2012 Chinese Physical Society

2 1, 4-,,. 2 Eppink [19,20].,, ( ),, [21] Pa He (paker, general valve), 1 mm (skimmer),.,,. (MCP) (PS). PS CCD (MS-2821E, Mintron) (PMT, 931 A, Hamamatsu),, (Model 611 Frame Grabber). (DG535, Stanford Research Systems). : Nd:YAG (YG981E10, Quantel) 355 nm, (LambdaPhysik, ScanMate2E OG), BBO. 25 cm,. (2+1)REMPI Br Br, 6p 4 P3/2 0 6p2 S1/2 0, nm nm. Doppler, ±0.005 nm. 1, 4- ( ), 99% 97%, , r v t : r = Nvt, (1) N, N,,.,,, [22 24]. 266 nm CH 3 I + hν CH 3 + I( 2 P 3/2 ) CH 3 + I( 2 P 1/2 ), (2) C I UV I ( 2 P 3/2 ) I ( 2 P 1/2 ). Parker 266 nm, v(i) = m/s [24]., 266 nm,,. 266 nm nm,,,. ( V E /V R ) I R ( pixel ). 1, pixel, t, Pixel-t, 2. 2 R-t, V 2300 V, pixel. Parker, pixel v(i) = m/s, (1), 3200 V

3 2300 V N = 1.13., V/2857 V 3200 V/2300 V 4,,,., Br Br P (v), 1, 4- C Br. 234 nm, Cl,, Cl C Cl,. (a) (b) 2400 V/1725 V 1600 V/1150 V 1 I ( ) R/pixel t 2 pixel( R) t 3.2 1, nm 1, nm Br Br, ,, P (v), , nm Br Br ( ) (a) Br ( nm); (b) Br ( nm), P (v), P (E): P (E) = P (v) dv de, (3) E T = 1 2 (m Br + m C4 H 8 Cl) m Br m C4 H 8 Cl v 2, (4) E T, m Br, m C4 H 8 Cl v,, C 4 H 8 Cl. : E avl = hv D 0 + E p int = E T + E int, (5) E avl = E avl E so = E T + E int, (6) f T = E T E avl, (7) E avl E avl, hν, D 0 C Br, 1, 4-, C Br 1, 3- C Br, 289 kj mol 1 [25]

4 , E p int. E so = 44 kj mol 1 - [26]., Br Br f T (a) Br ( nm) 1.0 (b) Br * ( nm) /arb. units /arb. units v/mss v/mss , 4- C 4 H 8 BrCl 234 nm Br (a) Br (b) 1 1, nm /nm E hv /kj mol 1 E avl /kj mol 1 v/ms 1 E T /kj mol 1 f T Br Br , [27].,.,,. 1, 4-.,, f T = 0.23, ( Br 0.19, Br 0.20), 1, 4-., 1, 4- C 4 H 8 Cl.,,,. 3 Br Br, Br Br.,, β, Br Br β , nm Br Br /nm β x // /% x /% Br ± Br ± , 1, 4- A n σ. Mulliken [28], A, 3 Q 0, 3 Q 1 1 Q 1. 3 Q 0 Br, C Br, ( β 2), 3 Q 1 1 Q 1 Br, C Br, ( β 1). Br Br β ,,, 1, 4- A

5 (x ) (x ), 2. Br β, 94%, 3 Q 0. Br β Br, 68% 32%. 3.3, 1, 4- ( [11], 1, 2- [14], 1, 3- [15] ) 234 nm. 5, 234 nm. 5,, f T. Br Br. Br,, f T , Br,, f T , ft=et/eavl CH 2 BrCl (CH 2 ) 2 BrCl Br * (234 nm) Br (234 nm) (CH 2 ) 3 BrCl (CH 2 ) 4 BrCl n 5 (CH 2 ) nbrcl(n = 1, 2, 3, 4) 234 nm,, f T. [29]. 248 nm,, f T , 266 nm f T 0.35 [30].,,,. (6) (7),, (E T ), (E int ).,, (f T ). 4,, 266 nm I, N = , nm, Br Br. 1, nm C Br,. Br Br, Br Br β ,.,, 1, 2-, 1, 3-1, nm,,,,.,. Gregor Knopp ;,

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7 Calibration of velocity map imaging system and photodissociation dynamics of 1, 4-C 4 H 8 BrCl Liu Yu-Zhu 1)2) Xiao Shao-Rong 1) Zhang Cheng-Yi 1) Zheng Gai-Ge 1) Chen Yun-Yun 1) 1) ( College of Physics and Opto-electronics Engineering, Nanjing University of Information Science & Technology, Nanjing , China ) 2) ( Paul Scherrer Institute, Villigen 5232, Switzerland ) ( Received 19 March 2012; revised manuscript received 1 April 2012 ) Abstract Depletion of atmospheric ozone layers is more and more serious. Alkyl halides dissociate under the solar UV radiation with the product of free halogen atoms, which greatly damages the ozone layer and is the main culprit for the depletion of ozone layers. In this paper, methyl iodide is chosen as a calibration system of velocity map imaging. Velocity map images of iodine atom I ( 2 P 3/2 ) at different focus voltages are obtained in the dissociation of methyl iodine under an UV radiation of 266 nm by techniques of velocity map imaging and REMPI (Resonance Enhanced Multiphoton Ionization). The magnification factor N of velocity map imaging system is measured to be Photodissociation dynamics of 1, 4-C 4H 8BrCl under an UV radiation of 234 nm is investigated on this velocity map imaging system. The speed and angular distributions of the fragments Br( 2 P 3/2 ) and Br ( 2 P 1/2 ) atoms in the dissociation are obtained and analyzed. Experimental results suggest that the dissociation of 1, 4-C 4H 8BrCl to both Br( 2 P 3/2 ) and Br ( 2 P 1/2 ) atoms under an UV radiation of 234 nm happens promptly along the C-Br bond via repulsive surfaces after excitation. The anisotropy coefficient β values are obtained from angular distributions of imaging of the fragments Br ( 2 P 3/2 ) and Br ( 2 P 1/2 ) atoms, by which the ratio between perpendicular transition and parallel transition for those two dissociation channels are calculated. In addition, photodissociation mechanisms of CH 2BrCl, 1, 2-C 2H 4BrCl, 1, 3-C 3H 6BrCl and 1, 4-C 4H 8BrCl at an UV radiation of 234 nm are compared, and the dependences of dissociation mechanisms of dihalogen alkyl compounds on size of the alkyl radical are obtained. Keywords: 1, 4-C 4 H 8 BrCl, photodissociation, velocity map imaging, system calibration PACS: Gj, Lg, Ms, Lp * Project supported by the Scientific Research Foundation of Technology Support Program of Jiangsu Province (Grant No. BE ), and the Nanjing University of Information Science & Technology (Grant No ). yuzhu.liu@psi.ch