K. R. Leopold

The structure of NH3–acetylene

The microwave spectrum of the weakly bound complex NH3–acetylene has been measured by molecular beam electric resonance spectroscopy. A spectrum characteristic of a symmetric top is observed and the following spectroscopic constants are determined:  The observed spectrum is consistent with an axially symmetric complex in which the acetylene hydrogen bonds to the ammonia with a hydrogen bond length of 2.33 A.

Rotational spectrum and structure of the complex HCNCO2

Radiofrequency and microwave rotational spectra of the complexes HCN CO2 and DCN CO2 have been obtained using molecular beam electric resonance spectroscopy. The spectra are characteristic of prolate asymmetric rotors. The spectroscopic constants obtained are These are shown to be consistent with a C2v structure in which the nitrogen of the HCN bonds to the carbon of the CO2 with a weak bond length of 3.00 A. The HCN subunit subtends an average angle of 17.4 (2)° with the line joining the centers of mass of the two submolecules, and the average bending vibrational amplitude of the CO2 is 11(1)°. The difference between the average amplitudes of the in‐plane and out‐of‐plane bending vibrations of the HCN is less than 4°. The stretching force constant for the weak bond is 0.049 mdyne/A in HCNCO2, and the induced dipole moment is 0.361 D.

The rotational spectrum and structure of NH3–HCN

The microwave spectrum of H3N–HCN has been measured using the molecular beam electric resonance technique. A symmetric top spectrum is observed and the following spectroscopic constants were obtained::[RW2:B0(MHz):3016.756 1(24)]

Microwave and radiofrequency Stark spectrum of ArHCN: A highly nonrigid molecule

The rotational spectrum of the weakly bound complex ArHCN has been observed using molecular beam electric resonance spectroscopy. The spectrum is superficially characteristic of that of a linear molecule with both unusually large centrifugal distortion (requiring a J6 dependent distortion term to fit the data) and an unexpectedly large bending amplitude. The spectroscopic constants are The centrifugal distortion constant DJ is remarkably large and abnormally sensitive to isotopic substitution. Using the usual model, the stretching and bending force constants obtained from these data are an order of magnitude smaller than those similarly computed for the hydrogen halide complexes of argon. The calculated stretching and bending frequencies are 10 cm−1, predicting that excited vibrational levels should be populated in the beam. Three transitions have been observed which appear to correspond to an excited vibrational level of ArDCN, but poor signal‐to‐noise has prohibited their unambiguous assignment. W...

The rotational spectrum, internal rotation, and structure of NH3–CO2

The radio frequency and microwave spectra of NH3–CO2 have been measured using the molecular beam electric resonance technique. The spectrum is characteristic of an asymmetric top in which the NH3 subunit exhibits effectively free internal rotation. The spectroscopic constants obtained for the ground internal rotor state are presented below: (B+C/2) (MHz)  3756.178(3),  (B−C/2) (MHz)  597.4(2), A−(B+C/2) (MHz)  8035.(8),  ΔJ (MHz)  0.0240(4), δK (MHz)  0.20(2),  ΔJK  (MHz)  0.23(5), δJ (MHz)  0.007(1),  eQqaa (MHz)  −3.175(4), eQqbb (MHz)  1.557(9),  eQqcc (MHz)  1.617(11),  μ(D)  1.7684(14). The N–CO2 framework of the complex has C2v symmetry with a N–C weak bond length of 2.9875(4) A. The average bending angle of the NH3 subunit is 22.71(5)° with a difference in amplitude of 1.0(4)° between the in plane and out of plane excursions. The weak bond stretching force constant is 0.070(1) mdyn/A and the induced dipole moment is 0.411(2) D. (B+C)/2 for the first excited internal rotor state (‖m‖=1) is 3753.008(...

Rotational spectrum and structure of the complex Ar–CH3CN

The microwave spectrum of the weakly bound complex Ar–CH3CN has been observed using a pulsed‐nozzle Fourier‐transform microwave spectrometer. The spectrum is characteristic of an asymmetric rotor with nearly free internal rotation of the methyl group. Spectroscopic constants for the ground internal rotor state, in megaHertz, are 3:[RW3:A=9323.7769(22),:B+C=3439.5578(15),:B–C=326.6860(12)].