Fourier Transform Limited IR Source
Final Report Abstract
The main theme of our research is to study molecule-surface interaction at a very fundamental level, focussing on the conversion of energy between translational, vibrational and rotational motion of the molecule, and phonon and electron-hole pair excitation of the solid. In particular, collision-induced vibrational excitation and relaxation are known to be strongly influenced by nonadiabatic effects, i.e. coupling between nuclear and electronic motion. We use crystalline surfaces under ultra-high vacuum, molecular beams, and various laser-based detection schemes to extract state-to-state vibrational excitation and relaxation probabilities. In the context of such experiments, the Fourier transform limited IR source is used for vibrational overtone pumping of diatomic molecules, specifically NO, CO and HCl. With NO, the system was used to pump the X2 Π v=0→2 and v=0→3 transitions. The required wavelengths near 2.68 µm (3729 cm^-1) and 1.80 µm (5549 cm^-1) were generated as the idler and signal wave, respectively, of the optical parametric amplification stage of the laser system. With CO, it was used to pump the X1 ∑+ v=0→2 transition with wavelengths near 2.35 µm (4264 cm^-1). Currently, the system is being used with HCl molecules to pump the X1 ∑+ v=0→1 and v=0→2 transitions with wavelengths near 3.44 µm (2906 cm^-1, idler) and 1.76 µm (5688 cm^-1, signal), respectively. For all of these systems, the narrow linewidth of the Fourier transform limited IR source, measured as 130±10 MHz, is essential to obtaining high pumping efficiency. Scientifically, vibrational overtone pumping has served three different purposes: 1. Many of the phenomena under study depend on the translational energy of the incident molecule when it hits the surface. The velocities of molecules in the molecular beam can be tuned by using different carrier gases and varying their concentrations. The velocity distributions were measured using a time-of-flight technique, where vibrational overtone excitation is used for "tagging” molecules in the beam. These molecules are then state-specifically detected using a pulsed dye laser for resonant ionization (REMPI). The velocity of the molecules is determined with high accuracy from the spatial offset and temporal delay between the two laser pulses. 2. State-to-state measurements of collision-induced vibrational relaxation carry complementary information about the nonadiabatic coupling between vibrational and electronic degrees of freedom, with much higher signal-to-noise ratio than vibrational excitation measurements. For these experiments, vibrational overtone pumping is used to prepare incident NO molecules in vibrationally excited states v=2,3. After scattering from the surface, their rotational and vibrational state distributions are probed using REMPI. In addition, translational energy distributions can be measured with a time-of-flight technique, providing information on the coupling between translation, vibration and rotation. 3. Steric effects in molecule-surface collision were investigated by measuring vibrational relaxation probabilities in NO scattering from Au(111), with controlled orientation of the NO molecules at the instant of collision with the surface. Orientation was achieved with a recently developed technique, optical state selection with adiabatic orientation in a strong electric field. In these experiments, vibrational overtone pumping is used to prepare NO molecules in one or the other component of the X2 Π v=3 e/f ∆ doublet - these states evolve into oriented states as the molecule enters the electric field. The narrow linewidth of the Fourier transform limited IR source is essential here as the splitting of the two components is only ~900 MHz.
Publications
- Multiquantum Vibrational Excitation of NO Scattered from Au(111): Quantitative Comparison of Benchmark Data to Ab Initio Theories of Nonadiabatic Molecule-Surface Interactions. Angewandte Chemie 124 (20), 5038-5042, 2012
Russell Cooper, Christof Bartels, Alexander Kandratsenka, Igor Rahinov, Neil Shenvi, Kai Golibrzuch, Zhisheng Li, Daniel J. Auerbach, John C. Tully, and Alec M. Wodtke:
(See online at https://doi.org/10.1002/ange.201201168) - On the determination of absolute vibrational excitation probabilities in molecule-surface scattering: Case study of NO on Au(111). J. Chem. Phys. 137, 064705, 2012
Russell Cooper, Zhisheng Li, Kai Golibrzuch, Christof Bartels, Igor Rahinov, Daniel J. Auerbach, and Alec M. Wodtke
(See online at https://doi.org/10.1063/1.4738596) - Vibrational excitation and relaxation of NO molecules scattered from a Au(111) surface. AIP Conf. Proc. 1501, 1330, 2012
Christof Bartels, Kai Golibrzuch, Alexander Kandratsenka, Russell Cooper, Igor Rahinov, Daniel J. Auerbach, and Alec M. Wodtke
(See online at https://doi.org/10.1063/1.4769695) - Experimental and Theoretical Study of Multi-Quantum Vibrational Excitation: NO(v=0^1,2,3) in Collisions with Au(111). J. Phys. Chem. A 117 (32), 7091-7101,2013
Kai Golibrzuch, Alexander Kandratsenka, Igor Rahinov, Russell Cooper, Daniel J. Auerbach, Alec M. Wodtke, and Christof Bartels
(See online at https://doi.org/10.1021/jp400313b) - Observation of direct vibrational excitation in gas-surface collisions of CO with Au(111): a new model system for surface dynamics. Phys. Chem. Chem. Phys. 15, 1863-1867, 2013
Tim Schäfer, Nils Bartels, Kai Golibrzuch, Christof Bartels, Hansjochen Köckert, Daniel J. Auerbach, Theofanis N. Kitsopoulos, and Alec M. Wodtke
(See online at https://doi.org/10.1039/C2CP43351F) - Observation of orientation-dependent electron transfer in molecule-surface collisions. PNAS 110 (44), 17738-17743, 2013
Nils Bartels, Kai Golibrzuch, Christof Bartels, Li Chen, Daniel J. Auerbach, Alec M. Wodtke, and Tim Schäfer:
(See online at https://doi.org/10.1073/pnas.1312200110) - State-to-State Time-of-Flight Measurements of NO Scattering from Au(111): Direct Observation of Translation-to-Vibration Coupling in Electronically Nonadiabatic Energy Transfer. J. Phys. Chem. A 117 (36), 8750-8760, 2013
Kai Golibrzuch, Pranav R . Shirhatti, J an Altschäffel, Igor Rahinov, Daniel J. Auerbach, Alec M. Wodtke, and Christof Bartels
(See online at https://doi.org/10.1021/jp403382b) - Dynamical steering in an electron transfer surface reaction: Oriented NO(v=3, 0.08
Nils Bartels, Kai Golibrzuch, Christof Bartels, Li Chen, Daniel J. Auerbach, Alec M. Wodtke, and Tim Schäfer
(See online at https://doi.org/10.1063/1.4863862) - Electron hole pair mediated vibrational excitation in CO scattering from Au(111): Incidence energy and surface temperature dependence. J. Chem. Phys. 141, 124704, 2014
Pranav R. Shirhatti, Jörn Werdecker, Kai Golibrzuch, Alec M. Wodtke, and Christof Bartels:
(See online at https://doi.org/10.1063/1.4894814) - Incidence energy dependent state-to-state time-of-flight measurements of NO(v=3) collisions with Au(111): the fate of incidence vibrational and translational energy. Phys. Chem. Chem. Phys. 16, 7602,2014
Kai Golibrzuch, Pranav R. Shirhatti, Igor Rahinov, Daniel J. Auerbach, Alec M. Wodtke, and Christof Bartels
(See online at https://doi.org/10.1039/C3CP55224A) - The importance of accurate adiabatic interaction potentials for the correct description of electronically nonadiabatic vibrational energy transfer: A combined experimental and theoretical study of NO(v=3) collisions with a Au(111) surface. J. Chem. Phys. 140, 044701, 2014
Kai Golibrzuch, Pranav R. Shirhatti, Igor Rahinov, Alexander Kandratsenka, Daniel J. Auerbach, Alec M. Wodtke, and Christof Bartels
(See online at https://doi.org/10.1063/1.4861660)
