Photodissociation of 2-Bromobutane by Ion-velocity Map Imaging Technique

Abstract

The photodissociation dynamics of 2-bromobutane has been investigated at 233.62 and 233.95 nm by ion-velocity map imaging technique coupled with resonance-enhanced multiphoton ionization. The speed and angular distribution of Br and Br * fragments were determined from the map images. The two Gaussian components, shown in the speed distributions of Br and Br * atoms, are suggested to attribute to the two independent reaction paths of photodissociation for 2-bromobutane at 233.62 and 233.95 nm. The high-energy component is related to the prompt dissociation along the C−Br stretching mode, and the low-energy component to the dissociation from the repulsive mode with bending and C−Br stretching combination. The contributions of the excited 3 Q 0 , 3 Q 1 , and 1 Q 1 states to the products (Br and Br *) were discussed. Relative quantum yield of 0.924 for Br(2 P 3/2) at about 234 nm in the photodissociation of 2-bromobutane is derived.

Photodissociation of 2-Bromobutane at ∼265 nm by Ion-velocity Map Imaging Technique

“…At ∼234 nm the speed distributions of Br and Br * can be fitted with two Gaussian curves [23]. Moreover, the high-E t Gaussian is related to the direct dissociation along the C−Br bond, and the low-E t component to the dissociation from the repulsive mode with bending and C−Br stretching combination [23]. The high-E t Gaussian of Br accounts for 66% of the sum of two Gaussian components [23].…”

“…In our experimental, for Br and Br * in the photodissociation of 2-C 4 H 9 Br at ∼265 nm, the values of E t /E avl are 0.36 and 0.38 (see Table I), respectively, which are much lower than the rigid limit and close to the soft radical limit. The photolysis of 2-bromobutane at ∼234 nm has been investigated by ion-velocity map imaging technique coupled with RIMPI in our recent work [23]. At ∼234 nm the speed distributions of Br and Br * can be fitted with two Gaussian curves [23].…”

“…The photolysis of 2-bromobutane at ∼234 nm has been investigated by ion-velocity map imaging technique coupled with RIMPI in our recent work [23]. At ∼234 nm the speed distributions of Br and Br * can be fitted with two Gaussian curves [23]. Moreover, the high-E t Gaussian is related to the direct dissociation along the C−Br bond, and the low-E t component to the dissociation from the repulsive mode with bending and C−Br stretching combination [23].…”

“…Moreover, the high-E t Gaussian is related to the direct dissociation along the C−Br bond, and the low-E t component to the dissociation from the repulsive mode with bending and C−Br stretching combination [23]. The high-E t Gaussian of Br accounts for 66% of the sum of two Gaussian components [23]. In the present work, however, at ∼265 nm the speed distributions of Br and Br * can be fitted with only one Gaussian curves (high-E t Gaussian) which are related to direct dissociation channels.…”

“…In recent years, the time-sliced ion velocity imaging technique [5−7] combined with resonance-enhanced multiphoton ionization (REMPI) has been widely used to study the photodissociation of alkyl halides [8−22], such as CH 3 Br [14], C 2 H 5 Br [15], iso-C 3 H 7 Br [16], n-C 4 H 9 Br [17], iso-C 4 H 9 Br [18], and tert-C 4 H 9 Br [18]. Following our recent study on the photolysis of 2-bromobutane at 233.62 and 233.95 nm (∼234 nm) [23], the present work aims to study the photolysis of 2-bromobutane at 264.77 and 264.86 nm (∼265 nm) using ion-velocity map imaging technique coupled with REMPI. With the aid of the speed and angular distribution of Br and Br * fragments measured from the map images at ∼265 nm, the photodissociation paths and the contributions of the excited 3 Q 0 , 3 Q 1 , and 1 Q 1 states to produce Br and Br * have been studied for 2-C 4 H 9 Br.…”