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We investigate carbon isotope effects on the infrared bands of a laboratoryanalogue of carbonaceous dust, the quenched carbonaceous composite (QCC),synthesized from a plasma gas of methane with various 12C/13C ratios. Peakshifts to longer wavelengths due to the substitution of 12C by 13C are clearlyobserved in several absorption bands. The shifts are almost linearlyproportional to the 13C fraction. New features associated with 13C are notseen, indicating that the infrared bands in the QCC are not very localizedvibration modes but come from vibrations associated with rather large carbonstructures. An appreciable peak shift is detected in the 6.2 micron band, whichis attributed to a carbon-carbon vibration. A peak shift in an out-of-planebending mode of aromatic C--H at 11.4 micron is also observed, while only asmall shift is detected in the 3.3 micron band, which arises from a C--Hstretching mode. The present experiment suggests that peak shifts in theunidentified infrared (UIR) bands, particularly in the 6.2 micron band, shouldbe detectable in celestial objects with low 12C/13C ratios (< 10). The isotopicshifts seen in the QCC are discussed in relation to the variations in the UIRband peaks observed in post-asymptotic giant branch stars and planetarynebulae. The observed peak shift pattern of the UIR bands is qualitatively inagreement with the isotopic shifts in the QCC except for the 7.7 micron bandcomplex although the observed shifts in the UIR bands are larger than thoseinferred from derived isotope ratios for individual objects. The presentinvestigation suggests that part of the observed variations in the UIR bandpeaks may come from the isotopic effects.Comment: 12 pages, 7 figures, Accepted for Publication in A&

$\mathsf{^{13}}$C isotope effects on infrared bands of quenched carbonaceous composite (QCC)