Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany.
Phys Chem Chem Phys. 2012 May 21;14(19):7076-89. doi: 10.1039/c2cp40349h. Epub 2012 Apr 10.
Excitation of tert-butylnitrite into the first and second UV absorption bands leads to efficient dissociation into the fragment radicals NO and tert-butoxy in their electronic ground states (2)Π and (2)E, respectively. Velocity distributions and angular anisotropies for the NO fragment in several hundred rotational and vibrational quantum states were obtained by velocity-map imaging and the recently developed 3D-REMPI method. Excitation into the well resolved vibronic progression bands (k = 0, 1, 2) of the NO stretch mode in the S1← S0 transition produces NO fragments mostly in the vibrational state with v = k, with smaller fractions in v = k- 1 and v = k- 2. It is concluded that dissociation occurs on the purely repulsive PES of S1 without barrier. All velocity distributions from photolysis via the S1(nπ*) state are monomodal and show high negative anisotropy (β≈-1). The rotational distributions peak near j = 30.5 irrespective of the vibronic state S1(k) excited and the vibrational state v of the NO fragment. On average 46% of the excess energy is converted to kinetic energy, 23% and 31% remain as internal energy in the NO fragment and the t-BuO radical, respectively. Photolysis via excitation into the S2← S0 transition at 227 nm yields NO fragments with about equal populations in v = 0 and v = 1. The rotational distributions have a single maximum near j = 59.5. The velocity distributions are monomodal with positive anisotropy β≈ 0.8. The average fractions of the excess energy distributed into translation, internal energy of NO, and internal energy of t-BuO are 39%, 23%, and 38%, respectively. In all cases ∼8500 cm(-1) of energy remain in the internal degrees of freedom of the t-BuO fragment. This is mostly assigned to rotational energy. An ab initio calculation of the dynamic reaction path shows that not only the NO fragment but also the t-BuO fragment gain large angular momentum during dissociation on the purely repulsive potential energy surface of S2.
叔丁基亚硝酸盐被激发到第一和第二紫外吸收带中，分别导致在其电子基态（2）Π和（2）E 中有效地离解成碎片自由基 NO 和叔丁氧基。通过速度映射成像和最近开发的 3D-REMPI 方法，获得了数百个转动和振动量子态中 NO 碎片的速度分布和角各向异性。在 S1←S0 跃迁中，NO 伸展模式的良好分辨的振子带（k=0，1，2）的激发产生的 NO 碎片主要处于 v=k 的振动态，而 v=k-1 和 v=k-2 的比例较小。得出的结论是，离解发生在没有势垒的 S1 的纯排斥势能面上。通过 S1（nπ*）态的光解产生的所有速度分布都是单模态的，并且表现出高的负各向异性（β≈-1）。无论激发的振动态 S1（k）如何，以及 NO 碎片的振动态 v 如何，转动分布都在 j=30.5 附近达到峰值。平均有 46%的过剩能量转化为动能，23%和 31%分别留在 NO 碎片和叔丁氧基自由基中。在 227nm 处通过激发到 S2←S0 跃迁的光解产生的 NO 碎片在 v=0 和 v=1 中具有大致相等的人口。转动分布在 j=59.5 附近具有单个最大值。速度分布是单模态的，各向异性为β≈0.8。过剩能量分配到平移、NO 的内部能量和叔丁氧基的内部能量的平均分数分别为 39%、23%和 38%。在所有情况下，∼8500cm（-1）的能量仍然存在于叔丁氧基碎片的内部自由度中。这主要归因于旋转能量。动态反应路径的从头计算表明，不仅 NO 碎片，而且叔丁氧基碎片在 S2 的纯排斥势能面上离解时也获得了大的角动量。
