Search results for "rotational spectroscopy"
showing 10 items of 53 documents
Quantum effects and orientational ordering in adsorbed layers of linear molecules
1994
We study the influence of quantum fluctuations on the herringbone transition in adsorbed complete √3-mono-layers of diatomic molecules. Using Path-Integral Monte Carlo simulations for rotations, we can quantify the shift of the transition temperature for a highly realistic model to describe N2 on graphite. In addition, the zero-point motion of the librating molecules depresses the ground-state order parameter. We compare the benchmark data to quadratic Feynman-Hibbs effective potential simulations and to a quasiharmonic approximation. Using a simplified model for this transition, we study systematically quantum effects being relevant for lighter molecules. Depending on the rotator's rotatio…
Breakdown of the Reduction of the Rovibrational Hamiltonian: The Case of S18O2F2
2009
Abstract The ground state rotational spectrum of the near-spherical top molecule S18O2F2 (sulfuryl fluoride) has been measured from 50 to 700 GHz. As for the parent isotopologue, S16O2F2 [K. Sarka, J. Demaison, L. Margules, I. Merke, N. Heineking, H. Burger, H. Ruland, J. Mol. Spectrosc. 200 (2000) 55–64], it was necessary to use a non-reduced Hamiltonian in order to obtain a satisfactory fit. It was possible to determine six quartic centrifugal distortion constants (instead of five for a standard asymmetric top) and five sextic constants (one of them not existing in the reduced Hamiltonian) could also be determined. This ground state level has also been analysed thanks to a tensorial forma…
The semi-experimental equilibrium structures of AlCCH and AlNC
2015
Abstract Based on experimental rotational constants available in the literature (Walker and Gerry, Chem. Phys. Lett. 278, 9 (1997); Walker et al., J. Mol. Spectrosc. 209, 178 (2001); Sun et al., Chem. Phys. Lett. 553, 11 (2012)) [14,17,19] for five isotopologues of AlCCH and three isotopologues of AlNC as well as quantum-chemical computations for the vibrational corrections to rotational constants, the semi-experimental structures of these two aluminum compounds are determined. These empirical equilibrium structures (AlCCH: r e (Al C) = 1.957 A, r e (C C) = 1.222 A, r e (C H) = 1.065 A; AlNC: r e (Al N) = 1.850 A, r e (N C) = 1.181 A) compare favorably with theoretical best-estimate structu…
Dynamics of heavy fermions: Drude response in and
2006
While the effective mass of heavy fermions governs their thermodynamics, the optical properties are dominated by the characteristic relaxation rate which is expected to scale inversely with the effective mass. At the relaxation rate clear features, the so-called Drude response occur in the real and imaginary parts of the complex conductivity. Conventional optical spectroscopy can only indirectly probe the Drude response; thus we use novel broadband microwave spectroscopy to directly measure the frequency-dependent conductivity of UPd2Al3 and UNi2Al3 in the relevant frequency range and unambiguously observe the full low-energy electrodynamics of the heavy fermions including the Drude respons…
PRECISE LABORATORY MEASUREMENTS OF TRANS-DCOOH AND TRANS-HCOOD FOR ASTROPHYSICAL OBSERVATIONS
2011
The rotational spectra of the mono-deuterated isotopologues of trans-formic acid, trans-DCOOH and trans-HCOOD, were investigated. In the millimeter- and submillimeter-wave frequency regions the Lamb-dip technique was exploited to obtain sub-Doppler resolution and to resolve the hyperfine structure due to the deuterium and hydrogen nuclei, thus enabling the accurate determination of the corresponding hyperfine constants. The experimental determination was supported by high-level quantum-chemical calculations at the coupled-cluster level of theory using large atomic-orbital basis sets. The Lamb-dip measurements were also supplemented by THz Doppler- limited measurements in order to extend the…
Laser-microwave spectroscopy of the hyperfine structure of 9Be for the investigation of unstable Be isotopes
1997
Abstract For an investigation concerning the nuclear magnetic moments and their distributions in the nuclei of 7,11Be, an experimental project using laser-microwave double resonance spectroscopy for trapped ions is under progress at INS. Laser cooled ion crystals consisting of a few 9Be+ ions were observed and the ground state hyperfine splitting of 9Be+ was measured with a precision of 10−5. Experiments on the unstable isotope 7Be have been started.
Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure.
2011
Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 A and rSi-S = 1.9133 A) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected fi…
The magnetic hyperfine structure in the rotational spectrum of H2CNH
2010
Abstract The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64–172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the 14N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters.
The rotational gas-phase spectrum of trans- and cis-HSSOH at 100GHz
2009
Abstract We present the first pure rotational spectra of the two most stable conformers of oxatrisulfane, trans- and cis-HSSOH, in their vibrational ground state. For both conformers a-, b-, and c-type transitions have been recorded in the range from 75 to 120 GHz using an all solid-state spectrometer. More than 200 lines have been assigned for each conformer, most of them belonging to the r Q 2 - and the r Q 3 -branch of the perpendicular spectra. The least-squares fit analysis using a semirigid rotor Hamiltonian in S-reduction yields precise values for the ground-state rotational constants A 0 = 21 145.93422 ( 66 ) , B 0 = 4479.92301 ( 21 ) , C 0 = 3828.34269 ( 21 ) for cis-HSSOH, and A 0…
Microwave spectroscopy on heavy-fermion systems: probing the dynamics of charges and magnetic moments
2013
Investigating solids with light gives direct access to charge dynamics, electronic and magnetic excitations. For heavy fermions, one has to adjust the frequency of the probing light to the small characteristic energy scales, leading to spectroscopy with microwaves. We review general concepts of the frequency-dependent conductivity of heavy fermions, including the slow Drude relaxation and the transition to a superconducting state, which we also demonstrate with experimental data taken on UPd2Al3. We discuss the optical response of a Fermi liquid and how it might be observed in heavy fermions. Microwave studies with focus on quantum criticality in heavy fermions concern the charge response, …