Ultrafast Quantum Control in Molecules

我们周围物质的广泛性质(它们不同的颜色和气味，它们的味道，易燃性，溶解性，手感，毒性)与定义物质分子的原子的不同物理排列密切相关。当阳光漂白衬衫或阿司匹林缓解头痛时，分子结构的变化是有原因的。物理学家将分子中原子的这些排列建模为等高线图中的位置，该等高线被称为“能量景观”或“势能面”。稳定的原子排列(例如，有色染料分子的原子排列)位于能量景观的山谷中。化学变化，如阳光漂白衣物染料所需的变化，是原子位置从一个山谷到另一个山谷的旅程。这项美国国家科学基金会的研究项目提出了一种利用激光引导分子旅程的新方法。光不会移动原子，但它可以做一些更好的事情：它可以改变能量格局的形状。就像在峡谷上修建一座桥或修建一条穿过山脉的隧道可以降低在陆地上旅行的难度一样，这种新的光致能源景观可以有促进特定化学变化的捷径。这个项目考察了能源景观中自然出现的十字路口上的光诱导捷径。这里的新想法是，这些交叉点附近的激光可以利用量子干涉来引导分子。这些交叉点被称为“锥形交叉点”。值得注意的预测是，通过改变激光的性质，分子将从十字路口的一条路径切换到另一条路径。这一关于光如何促进或抑制化学变化的基本科学理解可能会导致诸如光激活药物的应用。这个项目将研究由非Born-Oppenheimer(NBO)耦合和激光诱导的偶极耦合之间的干涉所带来的锥形交叉点(CI)附近轨迹的量子控制。选择的研究体系是单离子水的解离和双离子化乙炔的异构化。这些化合物之所以被选中，是因为它们是富含氢的小分子，具有大的NBO偶联和强偶极耦合。原子运动将通过使用可调谐真空紫外线辐射的高次谐波源电离中性水或乙炔来启动。控制场将是一个超快的红外激光脉冲。这些NBO和偶极矢量耦合的相对取向可以通过绘制解离碎片的动量图来推断，或者通过反应后使用第二个强红外激光脉冲的库仑爆炸成像来推断。我们的目标是通过NBO和偶极向量耦合之间的干扰来演示对输出通道的控制，如解离或异构化产率与耦合场的极化、场强和频率的关系。

The wide-ranging properties of substances around us (their different colors and smells, their taste, flammability, solubility, feel, toxicity) are tied closely to different physical arrangements of the atoms that define the molecules of the substance. When sunlight bleaches a shirt or aspirin relieves a headache, changes in molecular structure are responsible. Physicists model these arrangements of atoms in molecules as locations in a contour map called an "energy landscape" or a "potential energy surface." The stable atomic arrangements (the atomic arrangement for colored dye molecules, for example) are located in the valleys of the energy landscape. Chemical change, such as the change required to sun-bleach clothing dye, is a journey of the atomic positions from one valley to another. This NSF research project proposes a new way to guide the molecular journey by the use of laser light. Light doesn't move the atoms, but it can do something that is even better: it can change the shape of the energy landscape. Just like a bridge built over a gorge or a tunnel built through a mountain can reduce the difficulty of a journey over land, the new light-induced energy landscape can have shortcuts that encourage particular chemical changes. This project examines light-induced shortcuts at naturally occurring cross-roads in the energy landscapes. The new idea here is that laser light near these crossings, which are called "conical intersections," can employ quantum interference to guide the molecule. The remarkable prediction is that by changing the properties of the laser light, the molecule will switch from one path at the crossroads to the other. This basic scientific understanding about how light can encourage or inhibit chemical change could lead to applications such as light-activated pharmaceuticals.This project will investigate quantum control of trajectories nearby conical intersections (CIs), brought about by interference between the non-Born-Oppenheimer (NBO) couplings and laser-induced dipole couplings. The systems chosen for study are dissociation of singly ionized water and isomerization of doubly ionized acetylene. These are selected because they are hydrogen-rich small molecules with large NBO couplings and strong dipole couplings. The atomic motion will be launched by ionization of neutral water or acetylene using a high harmonics source of tunable vacuum ultraviolet radiation. The control field will be an ultrafast infrared laser pulse. The relative orientation of these NBO and dipole vector couplings can be inferred by mapping the momentum of dissociating fragments, or by Coulomb explosion imaging using a second intense infrared laser pulse following the reaction. The goal is to demonstrate control of the output channel via interference between NBO and dipole vector couplings, as revealed by the dependence of the dissociation or isomerization yield on the polarization, field strength, and frequency of the coupling field.