Abstract
We present far infrared spectra of the conformer A of tryptamine in the 200 to 500 cm-1 wavenumber range along with resonant photoionization spectra of the far-infrared excited conformer A of tryptamine. We show that single-far-infrared photon excited tryptamine has highly structured resonance enhanced multi-photon ionization spectra, revealing the mode composition of the S1-state. Upon multiple-far-infrared photon absorption, the resonance enhanced multi-photon ionization spectrum broadens allowing ion gain spectroscopy to be performed. In the ion gain spectrum we detect the fundamental far-infrared modes but also combination and overtone bands with high efficiency. The implications to dip spectroscopy using a free electron laser compared to more conventional light sources are discussed.
Highlights
Ion-dip and fluorescence-dip spectroscopy are powerful tools for recording molecular spectra from the microwave (MW)[1] over the far infrared,[2] the infrared (IR),[3,4] to the ultraviolet (UV)[5] region
IR ion-dip (IR-ID) spectra were recorded by scanning the far infrared (far-IR) laser while probing with a fixed UV laser
The far-IR pulse energy used influences the dynamics of IR absorption and intramolecular vibrational redistribution (IVR), as will be shown below
Summary
Ion-dip and fluorescence-dip spectroscopy are powerful tools for recording molecular spectra from the microwave (MW)[1] over the far infrared (far-IR),[2] the infrared (IR),[3,4] to the ultraviolet (UV)[5] region. The modulation of the population by the pump pulse is probed by a second laser pulse via resonant two-photon ionization (R2PI), laser induced fluorescence (LIF), or IR predissociation/photodissociation.[6,7] In most cases, the modulated state is the ground state, and the excited state (S1) and the ionic state (D0) can be investigated by this technique depending on the timing of the lasers.[8] Depopulation of the ground state results in a decreased ion or fluorescence signal (the so-called dip), if the pump and probe laser share a common ground state level These techniques are referred to either as MW-UV double resonance (DR) spectroscopy, IR ion-dip (IR-ID)/ IR-UV DR spectroscopy, or UV-UV DR spectroscopy in the literature. The latter is known as spectral hole-burning.[9,10]
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