Microwave - Infrared Double Resonance Spectrometer

双共振光谱学将在许多方面推动我们的高分辨率光谱学实验。在所提出的构型中，我们想要结合在微波/太赫兹频率范围内的旋转光谱和在红外波长范围内的自由振动光谱。一般的想法是通过一个辐射源来处理气相中的分子，以便产生非常敏感的和分子特有的信号。第二辐射源用于产生仅当两个光子寻址共同的分子态时才出现的差信号。DRS仪器的一个部分是最小频率范围为2.5-18 GHz的啁啾脉冲傅里叶变换光谱仪(CPFTS)。这种装置能够在一个啁啾激发脉冲中解决大多数分子在非常宽的带宽上的最低旋转态。我们实验室有产生宽带线性调频信号和记录自由感应衰变(FID)信号的电子设备，但缺少产生必要灵敏度的高功率放大器和强分子束，必须购买。在许多实验中，CPFTS的宽带信号用作非常灵敏的探测器信号。在第二部分中，来自窄线宽但可广泛调谐的量子级联激光器的辐射解决了与一个分子、一个特定的异构体或构象和/或该物种的特定振动状态相关的非振动能级。因此，有可能破译分子混合物的复杂光谱，即同时存在不同异构体、构象和振动态的实验。因此，DRS将有助于分析复杂有机分子的光谱，并最终在天体物理观测中找到这些物种。在我们在离子陷阱中进行的高度复杂的作用光谱实验中，微波/太赫兹和红外辐射源改变了它们的作用。IR QCL应用于创建实际上无背景的作用光谱信号，例如通过振动激发促进化学反应。微波/太赫兹光子被用来改变分子离子的转动布居，从而导致记录分子离子的转动光谱，否则很难或几乎不可能获得这些光谱。这样的DRS仪器在商业上还不是一成不变的，但现在可以从各个部件建造它，这将使我们的研究处于独特的位置。

Double resonance spectroscopy (DRS) shall advance our high-resolution spectroscopy experiments in many substantial ways. In the proposed configuration we want to combine rotational spectroscopy in the microwave/THz frequency range and ro-vibrational spectroscopy in the infrared wavelength regime. The general idea is to address molecules in the gas phase by one radiation source in order to create a very sensitive and molecule specific signal. The second radiation source is used to create a difference signal which only arises when the two photons address a common molecular state. One part of the DRS instrument is a chirped pulse Fourier Transform Spectrometer (CPFTS) with a minimum frequency range of 2.5 – 18 GHz. This setup is able to address the lowest rotational states of most molecules over a very wide bandwidth in one chirp excitation pulse. The electronics to create a broad band chirp signal and to record the free induction decay (FID) signal is available in our laboratory but high-power amplifiers and an intense molecular beam to create the necessary sensitivity are missing and shall be purchased. For many experiments the broad band signal of the CPFTS serves as a very sensitive detector signal. In the second part radiation from a narrow line width but widely tunable Quantum Cascade laser addresses a ro-vibrational level associated with one molecule, one specific isomer or conformer and/or a specific vibrational state of this species. Therefore, it becomes possible to decipher complex spectra of molecular mixtures, experiments where different isomers, conformers and vibrational states are present at the same time. Thus DRS will be instrumental in analysing spectra of complex organic molecules and finally finding those species in astrophysical observations. In our highly sophisticated action spectroscopy experiments in ion traps the microwave/THz and infrared radiation sources change their role. The IR QCL shall be used to create a practically background free action spectroscopy signal, e.g. by promoting a chemical reaction through vibrational excitation. The microwave/THz photon is used to change the rotational population which results in recording the rotational spectra of molecular ions which is extremely hard or practically impossible to acchieve otherwise. Such a DRS instrument is not available commercially in one piece but building it from pieces becomes now possible and will put our research in a unique position.