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Title: Probing phonon-rotation coupling in helium nanodroplets: Infrared spectroscopy of CO and its isotopomers

Abstract

We have recorded the R(0){nu}{sub CO}=1(leftarrow)0 IR spectrum of CO and its isotopomers in superfluid helium nanodroplets. For droplets with average size N > or approx. 2000 helium atoms, the transition exhibits a Lorentzian shaped linewidth of 0.034 cm{sup -1}, indicating a homogeneous broadening mechanism. The rotational constants could be deduced and were found to be reduced to about 60% of the corresponding gas-phase values (63% for the reference {sup 12}C {sup 16}O species). Accompanying calculations of the pure rotational spectra were carried out using the method of correlated basis functions in combination with diffusion Monte Carlo (CBF/DMC). These calculations show that both the reduction of the rotational B constant and the line broadening can be attributed to phonon-rotation coupling. The reduction in B is confirmed by path integral correlation function calculations for a cluster of 64 {sup 4}He atoms, which also reveal a non-negligible effect of finite size on the collective modes. The phonon-rotation coupling strength is seen to depend strongly on the strength and anisotropy of the molecule-helium interaction potential. Comparison with other light rotors shows that this coupling is particularly high for CO. The CBF/DMC analysis shows that the J=1 rotational state couples effectively to phonon states,more » which are only present in large helium droplets or bulk. In particular, they are not present in small clusters with n{<=}20, thereby accounting for the much narrower linewidths and larger B constant measured for these sizes.« less

Authors:
; ; ;  [1];  [2];  [3];  [4];  [2]
  1. Lehrstuhl fuer Physikalische Chemie II, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
  2. Department of Chemistry and Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720 (United States)
  3. (Germany)
  4. (Austria)
Publication Date:
OSTI Identifier:
20787912
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 73; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevB.73.054502; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION SPECTROSCOPY; ANISOTROPY; ATOMS; CARBON 12; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; CORRELATION FUNCTIONS; DIFFUSION; DROPLETS; ELECTRON-PHONON COUPLING; HELIUM; HELIUM 4; INFRARED SPECTRA; ISOTOPE EFFECTS; LINE BROADENING; LINE WIDTHS; MOLECULES; MONTE CARLO METHOD; OXYGEN 16; PATH INTEGRALS; PHONONS; POTENTIALS; ROTATION; ROTATIONAL STATES; SUPERFLUIDITY; VIBRATIONAL STATES

Citation Formats

Haeften, Klaus von, Rudolph, Stephan, Simanovski, Iaroslav, Havenith, Martina, Zillich, Robert E., Fraunhofer ITWM, 67663 Kaiserslautern, Institut fuer Theoretische Physik, Johannes Kepler Universitaet, A-4040 Linz, and Whaley, K. Birgitta. Probing phonon-rotation coupling in helium nanodroplets: Infrared spectroscopy of CO and its isotopomers. United States: N. p., 2006. Web. doi:10.1103/PHYSREVB.73.0.
Haeften, Klaus von, Rudolph, Stephan, Simanovski, Iaroslav, Havenith, Martina, Zillich, Robert E., Fraunhofer ITWM, 67663 Kaiserslautern, Institut fuer Theoretische Physik, Johannes Kepler Universitaet, A-4040 Linz, & Whaley, K. Birgitta. Probing phonon-rotation coupling in helium nanodroplets: Infrared spectroscopy of CO and its isotopomers. United States. doi:10.1103/PHYSREVB.73.0.
Haeften, Klaus von, Rudolph, Stephan, Simanovski, Iaroslav, Havenith, Martina, Zillich, Robert E., Fraunhofer ITWM, 67663 Kaiserslautern, Institut fuer Theoretische Physik, Johannes Kepler Universitaet, A-4040 Linz, and Whaley, K. Birgitta. Wed . "Probing phonon-rotation coupling in helium nanodroplets: Infrared spectroscopy of CO and its isotopomers". United States. doi:10.1103/PHYSREVB.73.0.
@article{osti_20787912,
title = {Probing phonon-rotation coupling in helium nanodroplets: Infrared spectroscopy of CO and its isotopomers},
author = {Haeften, Klaus von and Rudolph, Stephan and Simanovski, Iaroslav and Havenith, Martina and Zillich, Robert E. and Fraunhofer ITWM, 67663 Kaiserslautern and Institut fuer Theoretische Physik, Johannes Kepler Universitaet, A-4040 Linz and Whaley, K. Birgitta},
abstractNote = {We have recorded the R(0){nu}{sub CO}=1(leftarrow)0 IR spectrum of CO and its isotopomers in superfluid helium nanodroplets. For droplets with average size N > or approx. 2000 helium atoms, the transition exhibits a Lorentzian shaped linewidth of 0.034 cm{sup -1}, indicating a homogeneous broadening mechanism. The rotational constants could be deduced and were found to be reduced to about 60% of the corresponding gas-phase values (63% for the reference {sup 12}C {sup 16}O species). Accompanying calculations of the pure rotational spectra were carried out using the method of correlated basis functions in combination with diffusion Monte Carlo (CBF/DMC). These calculations show that both the reduction of the rotational B constant and the line broadening can be attributed to phonon-rotation coupling. The reduction in B is confirmed by path integral correlation function calculations for a cluster of 64 {sup 4}He atoms, which also reveal a non-negligible effect of finite size on the collective modes. The phonon-rotation coupling strength is seen to depend strongly on the strength and anisotropy of the molecule-helium interaction potential. Comparison with other light rotors shows that this coupling is particularly high for CO. The CBF/DMC analysis shows that the J=1 rotational state couples effectively to phonon states, which are only present in large helium droplets or bulk. In particular, they are not present in small clusters with n{<=}20, thereby accounting for the much narrower linewidths and larger B constant measured for these sizes.},
doi = {10.1103/PHYSREVB.73.0},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 5,
volume = 73,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2006},
month = {Wed Feb 01 00:00:00 EST 2006}
}