Proton tunnelling and nitro-group torsion in 2-nitromalonaldehyde
Abstract
The rotational spectra of the normal and O-monodeuterated species of 2-nitromalonaldehyde have been observed in the two lowest vibrational states (0+0–) due to the proton tunnelling and in several excited states due to the nitro-group torsion.
No evidence for interaction between the two vibrational modes has been observed.
The analysis of each vibrational state in isolation has shown a remarkable difference in the centrifugal distortion constants between the 0+ and 0– states of the proton tunneling for both isotopic species due to Coriolis coupling.
The use of a coupled Hamiltonian for the 0+ and 0– states of the OD species has allowed the determination of the energy separation between these states (ΔE01= 3.00 ± 0.02 cm–1), while for the H species a rough value of ΔE01= 35 ± 15 cm–1 has been obtained from relative intensity measurements.
Some considerations are given concerning the barrier to proton tunnelling.
From the variation of the inertial defect with torsional quantum number the value vtor= 81 ± 2 cm–1 has been calculated for nitro-group torsion. It agrees with the value vtor= 80 ± 20 cm–1 obtained from intensity measurements.