The rotational spectrum of nitrosobenzene in the first four excited states of the torsional vibration has been observed. The vibrational fundamental is at about 100 cm−1. The barrier to rotation around the C–N bond is 3.9±1 kcal/mole, based on relative intensity measurements. Variations in the inertia defect in the excited states are compared with theory. The next-lowest vibrational state is at about 220 cm−1 and is an in-plane vibration.

Articles you may be interested inMicrowave spectrum, barrier to internal rotation, structure, and dipole moment of methane selenol

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The microwave spectra of three isotopic species of cyclopropylphosphine have been analyzed. The conformation of the molecule is the symmetric one allowing maximum interaction of the lone pair electrons of phosphorus with the intra-annular orbitals of the cyclopropyl ring. A structure compatible with the observed moments of inertia yields, along with other parameters, a C-P bond distance of 1.834 A, distinctly shorter than that observed in other organic phosphine derivatives. The dipole moment is found to be 1.16 D.

The microwave spectra of C~NO and CDaNO have been observed and analyzed. The barriers to internal rotation are 1137±5 and 1095±7 cal/mole for CHaNO and CDaNO, respectively, a difference of 42 cal/mole which is thought to be real. The barriers were calculated by the internal-axis method with retention of higher terms in the usual Fourier expansion of the rotational energy and computation of the torsional integrals in the harmonic-oscillator approximation. The theoretical parameters were fitted to the data by a least-squares method and the uncertainties reported are standard deviations. Transitions having comparable Stark and quadrupole energies were used to calculate the dipole moment. Secular equations of second or third order were solved for each of the data points. The dipole moment components are I'a= 2.240±0.OO1 D, I'b=0.522±0.006 D, and I'total = 2.300±0.OO2 D. The quadrupole coupling constants of C~NO are 0.50± 0.16, -6.016±0.031, and 5.518±0.031 for the components along the a, b, and c axes, respectively. The corresponding values for CDaNO are 0.60±0.07, -6.007±0.020, and 5.41l±0.020. The N=O and C-N distances are not well determined by the data. The CNO angle is 112.6±1.0o.

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The microwave spectrum of β-propiolactone has been observed in the vibrational ground state and in the first four excited states of the ring-puckering vibrational mode. The variation of the rotational constants with vibrational quantum number and the relative intensities of the observed vibrational satellites indicate that the vibration is essentially harmonic with ν0=160 cm−1 and with no appreciable barrier at the planar configuration. The dipole moment is 4.17±0.03 D, with μa=3.67±0.03 D, μb=1.99±0.02 D, and μc=0 in both the ground and first excited states.

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