Molecular spectroscopy and theoretical chemistry (Halonen), Laboratory of
Physical Chemistry, Department of Chemistry, University of Helsinki
Computation, theory and laser experiments
Our theoretical and computational research is associated with molecular spectroscopy and surface
science problems. We are particularly interested in the spectroscopy of water containing complexes
which are important in many atmospheric phenomena such as greenhouse effect and aerosol
nucleation. Another major computational project concerns long-range interactions of coin-age
metals (Cu, Ag, and Au) and grapheme, which is hot topic in nanotechnology. We develop our own
quantum mechanical models and computer programs to simulate various properties of these
systems. State-of-the art quantum chemical calculations are employed to obtain potential energy
surfaces and accurate numerical methods such variational and Monte Carlo calculations are used to
obtain eigenvalues.
We are developing new laser spectroscopic methods, which we apply to spectroscopy, trace gas
analysis and medicine. We are currently putting significant effort on the development of midinfrared continuous-wave optical parametric oscillators (OPOs). The work has generated several
innovative methods for improved frequency tuning and control of the OPOs. The major results of the
work have been published in peer-reviewed scientific journals and conferences, with publications in
the two most highly ranked journals in the field of optics (Optics Letters and Optics Express). The
laser cavity ring-down experiments have been used to detect HCN, HCCH and NH3 directly in the
exhaled human air. We are able to observe very small concentrations, for example in the case of
HCCH as small as 150 parts per trillion in the volume.
Publications
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J.-P. Jalkanen, M. Halonen, D. Fernández-Torre, K. Laasonen and L. Halonen, A computational study of
the adsorption of small Ag and Au nanoclusters on graphite, J. Phys. Chem. A 111 (2007) 12317-12326.
T. Salmi, V. Hänninen, A. L. Garden, H. G. Kjaergaard, J. Tennyson and L. Halonen, Calculation of the
OH stretching vibrational overtone spectrum of the water dimer, J. Phys. Chem. A 112 (2008) 63056312.
E. Sälli, V. Hänninen and L. Halonen, Variationally calculated vibrational energy levels of ammonia
adsorbed on a Ni(111) surface, J. Phys. Chem. C 114 (2010) 4550–4556 (2010).
M. Siltanen, M. Vainio and L. Halonen, Pump-tunable continuous-wave singly resonant optical
parametric oscillator from 2.5 to 4.4 micrometers, Opt. Express 18 (2010)14087-14092 (2010).
M. Metsälä, F. M. Schmidt, M. Skyttä, O. Vaittinen and L. Halonen, Acetylene in breath: background
levels and real-time eliminations kinetics after smoking, J. Breath Res. 4 (2010) 046003/1-046003/8.