Sanford Todd, Han Sang-Yun, Thompson Matthew A, Parson Robert, Lineberger W Carl
JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA.
J Chem Phys. 2005 Feb 1;122(5):54307. doi: 10.1063/1.1839178.
We report the ionic photoproducts produced following photoexcitation of mass selected IBr(-)(CO(2))(n), n=0-14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states of the IBr(-) chromophore. Excitation of these states in IBr(-) leads to production of I(-)+Br and Br(-)+I( *), respectively. Potential energy curves for the six lowest electronic states of IBr(-) are calculated, together with structures for IBr(-)(CO(2))(n), n=1-14. Translational energy release measurements on photodissociated IBr(-) determine the I-Br(-) bond strength to be 1.10+/-0.04 eV; related measurements characterize the A(') (2)Pi(1/2)<--X (2)Sigma(1/2) (+) absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A(') (2)Pi(1/2) electronic state, IBr(-)(CO(2))(n) exhibits size-dependent cage fractions remarkably similar to those observed for I(2) (-)(CO(2))(n). In contrast, excitation to the B 2 (2)Sigma(1/2) (+) state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr(-)(CO(2))(8) determines the time required for recombination on the ground state following excitation to the A(') state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr(-) cluster ions, the time required for recombination is found to be approximately 5 ns, some three orders of magnitude longer than observed for the analogous I(2) (-) cluster ion. Comparisons are made with similar experiments carried out on I(2) (-)(CO(2))(n) and ICl(-)(CO(2))(n) cluster ions.
我们报告了在790和355 nm波长下对质量选择的IBr⁻(CO₂)ₙ（n = 0 - 14）团簇离子进行光激发后产生的离子光产物。这些波长为两个解离态提供单重态激发，分别对应于IBr⁻发色团的A′²Π₁/₂和B²Σ₁/₂⁺态。在IBr⁻中激发这些态分别导致产生I⁻ + Br和Br⁻ + I*。计算了IBr⁻的六个最低电子态的势能曲线，以及IBr⁻(CO₂)ₙ（n = 1 - 14）的结构。对光解离的IBr⁻进行平动能释放测量，确定I - Br⁻键强度为1.10±0.04 eV；相关测量表征了A′²Π₁/₂←X²Σ₁/₂⁺吸收带。测量了激发到A′²Π₁/₂和B²Σ₁/₂⁺态后光解离产物分布随团簇大小的变化。结果表明，溶剂驱动了诸如自旋 - 轨道弛豫、电荷转移、复合和基态振动弛豫等过程。激发到A′²Π₁/₂电子态后，IBr⁻(CO₂)ₙ表现出与I₂⁻(CO₂)ₙ中观察到的显著相似的尺寸依赖性笼分数。相比之下，激发到B²Σ₁/₂⁺态显示出在激发态中的广泛俘获，这主导了我们研究的所有团簇大小的复合行为。最后，对IBr⁻(CO₂)₈进行的泵浦 - 探测实验确定了激发到A′态后基态复合所需的时间。虽然光碎片实验表明对于该团簇离子及更大的IBr⁻团簇离子在基态电子态中有100%的复合，但发现复合所需的时间约为5 ns，比类似的I₂⁻团簇离子观察到的时间长约三个数量级。并与对I₂⁻(CO₂)ₙ和ICl⁻(CO₂)ₙ团簇离子进行的类似实验进行了比较。
