Sandia National Laboratories, Livermore, California 94550, USA.
J Chem Phys. 2011 Mar 7;134(9):091101. doi: 10.1063/1.3563016.
We report direct doubly differential (quantum state and angle-resolved) scattering measurements involving short-lived electronically excited molecules using crossed molecular beams. In our experiment, supersonic beams of nitric oxide and argon atoms collide at 90°. In the crossing region, NO molecules are excited to the A(2)Σ(+)state by a pulsed nanosecond laser, undergo rotationally inelastic collisions with Ar atoms, and are then detected 400 ns later (approximately twice the radiative lifetime of the A(2)Σ(+)state) by 1 + 1(') multiphoton ionization via the E(2)Σ(+) state. The velocity distributions of the scattered molecules are recorded using velocity-mapped ion imaging. The resulting images provide a direct measurement of the state-to-state differential scattering cross sections. These results demonstrate that sufficient scattering events occur during the short lifetimes typical of molecular excited states (∼200 ns, in this case) to allow spectroscopically detected quantum-state-resolved measurements of products of excited-state collisions.
我们报告了使用分子束交叉技术进行的涉及短寿命电子激发分子的直接双重微分（量子态和角度分辨）散射测量。在我们的实验中，一氧化氮和氩原子的超音速束在 90°处碰撞。在交叉区域，NO 分子被纳秒激光脉冲激发到 A(2)Σ(+)态，与 Ar 原子发生旋转非弹性碰撞，然后在 400 ns 后（大约是 A(2)Σ(+)态辐射寿命的两倍）通过 E(2)Σ(+)态的 1 + 1(')多光子电离被检测到。使用速度映射离子成像记录散射分子的速度分布。得到的图像提供了对状态到状态微分散射截面的直接测量。这些结果表明，在分子激发态的典型短寿命（在这种情况下约为 200 ns）期间发生了足够多的散射事件，从而允许对激发态碰撞产物进行光谱检测的量子态分辨测量。
