Author Institution: I. Physikalisches Institut, Universitat zu Koln, 50937 Koln, Germany; Universitat Kassel, Fachbereich 10 - Physik, 34132 Kassel, Germany; Institut fur Physikalische Chemie, Universitat Mainz, 55099 Mainz, Germany

Author Institution: I. Physikalisches Institut, Universitat zu Koln, 50937 Koln, Germany; Karlsruher Institut fur Technologie, Institut fur Nanotechnologie, 76021 Karlsruhe, Germany; Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, USA

Author Institution: I. Physikalisches Institut, Universitat zu Koln, 50937 Koln, Germany; Karlsruher Institut fur Technologie, Institut fur; Nanotechnologie, 76021 Karlsruhe, Germany; Center for Theoretical; Chemistry, Department of Chemistry and Biochemistry, The University of; Texas at Austin, Austin, Texas 78712, U.S.A

0022-2852/$ see front matter 2011 Elsevier Inc. A doi:10.1016/j.jms.2011.07.007 ⇑ Corresponding author. E-mail address: sthorwirth@ph1.uni-koeln.de (S. T Close inspection of the m3 fundamental vibrational mode of Si2C3 observed recently (Krieg et al., Rev. Sci. Instrum. 82 (2011) 063105) reveals the presence of another weak mode of which more than 40 rovibrational transitions have now been analyzed. Based on comparison against molecular parameters from high-level quantum chemical calculations this new series of lines is identified as the (m3+m7)-m7 hot band. 2011 Elsevier Inc. All rights reserved.

Close inspection of the ν3 fundamental vibrational mode of Si2C3 observed recently (Krieg et al., Rev. Sci. Instrum. 82 (2011) 063105) reveals the presence of another weak mode of which more than 40 rovibrational transitions have now been analyzed. Based on comparison against molecular parameters from high-level quantum chemical calculations this new series of lines is identified as the (ν3+ν7)-ν7 hot band.

A new high-resolution infrared spectrometer using an optical parametric oscillator working at 5 mu m as radiaton source has been assembled in the Cologne laboratory and is now operated routinely. As one of the first projects, we have reobserved the nu(3) vibrational fundamental (asymmetric C-C stretching mode) of Si2C3 located at 1968.2 cm(-1).

The nu(5) antisymmetric stretching mode of the linear carbon cluster C(7) has been revisited using a sensitive high-resolution spectrometer, including an external-cavity quantum cascade laser covering the range of interest of 1894-1901 cm(-1). 50 transitions of the nu(5)-band have been recorded and analyzed together with 45 transitions of the nu(4)-band measured by Neubauer-Guenther et al. [J. Chem. Phys. 127, 014313 (2007)]. We determined the band centers, rotational and centrifugal constants very precisely. In addition, 29 hot band transitions have been measured and tentatively assigned to the nu(5)+nu(11)-nu(11) hot band. A global fit of the hot bands nu(5)+nu(11)-nu(11) and nu(4)+nu(11)-nu(11) is presented. Derived l-type doubling constants allow for an experimental estimation of the nu(11)-band center.