Steeves Adam H, Bechtel Hans A, Coy Stephen L, Field Robert W
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Chem Phys. 2005 Oct 8;123(14):141102. doi: 10.1063/1.2069865.
We report a new form of microwave optical double-resonance spectroscopy called millimeter-wave-detected, millimeter-wave optical polarization spectroscopy (mmOPS). In contrast to other forms of polarization spectroscopy, in which the polarization rotation of optical beams is detected, the mmOPS technique is based on the polarization rotation of millimeter waves induced by the anisotropy from optical pumping out of the lower or upper levels of the millimeter wave transition. By monitoring ground-state rotational transitions with the millimeter waves, the mmOPS technique is capable of identifying weak or otherwise difficult-to-observe optical transitions in complex chemical environments, where multiple molecular species or vibrational states can lead to spectral congestion. Once a transition is identified, mmOPS can then be used to record pure rotational transitions in vibrationally and electronically excited states, with the resolution limited only by the radiative decay rate. Here, the sensitivity of this nearly-background-free technique is demonstrated by optically pumping the weak, nominally spin-forbidden CS e (3)Sigma(-)-X (1)Sigma(+) (2-0) and d (3)Delta-X (1)Sigma(+) (6-0) electronic transitions while probing the CS X (1)Sigma(+) (v(")=0,J(")=2-1) rotational transition with millimeter waves. The J(')=2,N(')=2<--J(')=1,N(')=1 pure rotational transition of the CS e (3)Sigma(-) (v(')=2) state is then recorded by optically preparing the J(')=1,N(')=1 level of the e (3)Sigma(-) (v(')=2) state via the J(')=1,N(')=1<--J(")=1 transition of the e (3)Sigma(-)-X (1)Sigma(+) (2-0) band.
我们报道了一种新形式的微波光学双共振光谱，称为毫米波探测的毫米波光学偏振光谱（mmOPS）。与其他形式的偏振光谱不同，其他形式的偏振光谱是检测光束的偏振旋转，而mmOPS技术基于由毫米波跃迁的较低或较高能级的光抽运引起的各向异性所导致的毫米波偏振旋转。通过用毫米波监测基态转动跃迁，mmOPS技术能够识别复杂化学环境中微弱的或难以观测到的光学跃迁，在这种环境中，多种分子种类或振动状态会导致光谱拥挤。一旦识别出一个跃迁，mmOPS就可用于记录振动和电子激发态下的纯转动跃迁，其分辨率仅受辐射衰减率限制。在此，通过光抽运微弱的、名义上自旋禁戒的CS e (3)Σ⁻-X (1)Σ⁺ (2-0)和d (3)Δ-X (1)Σ⁺ (6-0)电子跃迁，同时用毫米波探测CS X (1)Σ⁺ (v″=0,J″=2-1)转动跃迁，展示了这种几乎无背景技术的灵敏度。然后，通过经由e (3)Σ⁻-X (1)Σ⁺ (2-0)带的J′=1,N′=1←J″=1跃迁光制备e (3)Σ⁻ (v′=2)态的J′=1,N′=1能级，记录了CS e (3)Σ⁻ (v′=2)态的J′=2,N′=2←J′=1,N′=1纯转动跃迁。
