High resolution IR-diode laser jet spectroscopy of malonaldehyde

The ro-vibrational infrared spectrum of malonaldehyde has been measured for the first time at high resolution. Employing diode laser spectroscopy in a pulsed slit seeded He jet expansion the rotational structure of the ν6 (OH-bend/symmetric CC,CO stretch) fundamental could be completely resolved at a rotational temperature of about 7 K. The rotational structure of the (+) – tunnelling component was analyzed in terms of Watsonʹs semi-rigid rotor Hamiltonian with a band centre at 1594.0898 cm−1. Additional weaker signals were attributed to the (−) – tunnelling component. The estimated band centre around 1594.06 cm−1 corresponds to a reduction of the tunnelling splitting upon excitation of ν6 by only 0.03 cm−1.