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One System, Multiple Approaches
Published in Thomas C. Weinacht, Brett J. Pearson, Time-Resolved Spectroscopy, 2018
Thomas C. Weinacht, Brett J. Pearson
As with the other approaches, the experiment uses a UV pump pulse (270 nm, 11 fs) to launch a vibrational wave packet on the excited 1B state. A strong-field probe pulse (810 nm, 12 fs) then ionizes the molecule at different time delays. The laser pulses interact with the molecules in a vacuum chamber equipped with a time-of-flight mass spectrometer and microchannel plate detector for measuring the ion yield. Panel (a) of Figure 15.12 plots the parent ion yield (C6H8+) as a function of pump–probe delay. The data show a sharp increase in ion yield in going from negative to positive delays, followed by a decay with multiple features including a two time-step exponential decay and weak oscillations. The sharp increase in ion yield after time zero is due to the fact that the ionization potential in the excited state is much lower than from the ground state, leading to a higher yield after excitation by the pump pulse (the probe pulse intensity can be adjusted to minimize ionization from the ground state). Then, as the wave packet moves down the excited-state PES and undergoes internal conversion, the molecule progresses towards geometries where the ionization potential increases (leading to decay of the parent ion yield). Oscillations in the parent ion yield provide signatures of active vibrational modes along the reaction coordinate, and confirm the importance of these as predicted by theory.
Lasing to Ground State in Lilli at 13.5 nm
Published in S Svanberg, C-G Wahlström, X-ray Lasers 1996, 2020
D. V. Korobkin, C.H. Nam, S. Suckewer, A. Goltsov
The soft x–ray spectra were recorded with a 2.0 m, high resolution, grazing incidence spectrometer, SOXMOS [13], A microchannel plate detector, MCP, was gated for 20 nsec and synchronized with the PSP͠laser pulse. The crucial issue in the experiment was the very precise alignment of the axis of the microcapillary with the optical axis of the spectrometer and the PSP–laser beam. Without the initial plasma the PSP–laser propagated through the microcapillary without interacting with the walls.
Photoelectron angular distributions from resonant two-photon ionisation of adiabatically aligned naphthalene and aniline molecules
Published in Molecular Physics, 2021
Jacqueline Arlt, Dhirendra P. Singh, James O. F. Thompson, Adam S. Chatterley, Paul Hockett, Henrik Stapelfeldt, Katharine L. Reid
Schematics of the key elements in the experimental set-up are given in Figure 1(a,b). More details can be found in Ref. [30]. A molecular beam is formed by expanding a gas mixture of 80 bar of helium and 2 mbar of aniline or 1 mbar of naphthalene into a vacuum chamber through an Even-Lavie valve EL-7-4-2015-HRR,HT [31]. In the case of aniline (naphthalene), the valve was heated to 36°C (50°C). After passage through a 4-mm diameter skimmer, the molecular beam enters a velocity map imaging (VMI) spectrometer where it is crossed at 90° by two collinearly focused, pulsed laser beams, one to align the molecules and one to ionise them. The electrons produced by the ionisation pulse are extracted with the static electric field (140–150 V/cm) in the VMI spectrometer, and projected onto a two-dimensional imaging detector consisting of a microchannel plate detector with an active diameter of 41.5 mm backed by a phosphor screen; see Figure 1(b). The electron hits on the detector are recorded by a CCD camera (Prosilica GE 680, Allied Vision) and on-line software analysis determines and saves the coordinates of each individual electron hit. Thus, the basic experimental observables are two-dimensional velocity images of the photoelectrons. The repetition rate of the experiment is 200 Hz, limited by the pump speed in the vacuum chamber for the Even Lavie valve.
The adiabatic ionisation energy of CO2
Published in Molecular Physics, 2019
U. Hollenstein, K. Dulitz, F. Merkt
The PFI-ZEKE photoelectron spectra were recorded by monitoring the field-ionisation yield generated by the electric-field pulse sequence displayed in Figure 1(a) as a function of the laser wave number. The pulse sequence consisted of an initial, discrimination pulse of +66.4 mV/cm, followed by seven field-ionisation and electron-extraction pulses of −33.2, −41.5, −49.8, −58.1, −66.4, −74.7 and −83.0 mV/cm labelled 1–7 in the figure. For each laser-wave-number scan, seven PFI-ZEKE photoelectron spectra were obtained by integrating the electron signals over preset temporal gates corresponding to the arrival times on the microchannel-plate detector of the electrons generated by these seven pulses.
HDCO radical dissociation thresholds by velocity map imaging
Published in Molecular Physics, 2021
C. D. Foley, G. A. Cooper, J. Tu, M. Harmata, A. G. Suits
Ions produced by REMPI were accelerated through a time-of-flight tube by an ion optics assembly toward a 75 mm microchannel plate detector coupled to a P-47 phosphor screen (BOS-75-OPT01, Beam Imaging Solutions) for DC slice velocity map ion imaging with a 75 ns MCP pulse width [14,51,53,56]. Images were captured using a USB CCD camera (iDS uEye UI-2230SE-M-GL) and in-house data acquisition software NuACQ. A photomultiplier tube monitoring the phosphor screen obtained time-of-flight information. The experiment was performed at 10 Hz. Image reconstruction and data extraction were done using our finite slice analysis method, FinA [57,58].