Photolysis of 1‐C₄H₉I and 2‐C₄H₉I at 266 nm: Direct Observation of the Effect of Branching on the Photodissociation Mechanism

Abstract

Photodissociation dynamics of 1-C(4)H(9)I and 2-C(4)H(9)I at 266 nm is investigated by velocity ion imaging. Photodissociation channels of 1-C(4)H(9)I and 2-C(4)H(9)I are analyzed and compared. For 1-C(4)H(9)I the photodissociation dynamics only correlates with direct dissociation via repulsive surfaces. While for 2-C(4)H(9)I, a new formation channel of I and I* atoms is observed. It is attributed to the repulsive mode along the C-I stretch, coupled with some bending motions. As the alkyl group becomes more branched, the contribution of bending modes to I and I* is much more obvious in the photodissociation of 2-C(4)H(9)I than in that of 1-C(4)H(9)I. Additionally, the curve-crossing probability between (3)Q(0) and (1)Q(1) increases greatly with branching, from 0.31 for 1-C(4)H(9)I to 0.70 for 2-C(4)H(9)I in the prompt dissociation channel; the relative quantum yield for I* decreases strongly with branching, from 0.65 for 1-C(4)H(9)I to 0.28 for 2-C(4)H(9)I.

Near-UV photodissociation dynamics of CH2I2

“…Larger fractions of the available energy are partitioned into the alkyl radical fragments following photodissociation of larger alkyl iodides, although the propensity for production of I* over I remains and the analogous electronic states determine the photochemistry. 50,57 The long-wavelength photochemistry of CH 2 BrI is perhaps more directly comparable to CH 2 I 2 . 58 At 248 nm, dissociation to form CHBr + I dominates and the behavior is generally similar to CH 2 I 2 ; specifically, the transitions are predominantly parallel in character, the majority of the available energy is partitioned into the radical fragment, and the I/I* spin-orbit branching also favors the ground state.…”

Ultrafast photodissociation dynamics of n-butyl iodide in the A-band

“…In our previous paper [14], we have reported the effect of branching of α-carbon atom on photodissociation mechanisms of alkyl iodides, which is based on comparison of photodissociation dynamics of n-C 4 H 9 I and sec-C 4 H 9 I at ∼267 nm. As the alkyl group becomes more branched, the mixing of the bending motions about the α-carbon atom with the C-I stretching in the photodissociation of alkyl iodides becomes more significant.…”

Application and Improvement in the Ion Velocity Imaging of Threshold Photoelectron-Photoion Coincidence Measurements

“…由 于激发的能量较高, 解离后生成的 O + 离子具有较大 的平动能(约 1.2 eV). 为了确保其速度成像投影在 40 mm 直径的检测器表面, 以往光电离实验8,9,[20][21][22] 中 均采用了场强较强的引出电场(>100 V•cm -1 )和加速 电场, 而这样的场强显然很难在当前的 TPEPICO 实 验中应用. 如前所述, 当引出电场过强时, 会导致阈 值光电子的能量分辨率下降, 大量具有平动能的 "热" 电子与阈值光电子同时被电子探测器收集, 造 成很强的误符合事件信号.…”