William Klemperer

Radiofrequency and Microwave Spectrum of the Hydrogen Fluoride Dimer; a Nonrigid Molecule

The radiofrequency and microwave spectra of the K=0 states of (HF)2, (DF)2, and HFDF have been studied by the molecular beam electric resonance method. A unique hydrogen tunnelling motion involving the breaking and reforming of the hydrogen bond causes a splitting of rotational energy levels for (HF)2 and (DF)2, but not for HFDF. The electric dipole selection rules and nuclear spin statistics for the tunnelling molecules have been derived from a consideration of an extended permutation‐inversion group. Rotational constants, tunneling doublings, electric dipole moments, and deuterium quadrupole coupling constants have been determined from the observed spectra of the K=0 states. (HF)2(DF)2HFDF(B+C)/2 (MHz)6504.8±2.06252.194±0.0026500.1±0.1ν (MHz)19 776±121579.877 ±0.004μa  (D)2.987±0.0032.9919±0.00063.029±0.003(eqQ)Da (KHz)···110±8270±30 These results are interpreted with a semirigid, nonlinear model of the dimer geometry. The F—F distance is 2.79 ± 0.05 A, and the end hydrogen fluoride unit is bent from 60...

Hyperfine Structure Constants of HF and DF

The radio frequency spectrum of HF and DF is measured by the molecular‐beam electric resonance method. The measurements are in the lowest vibrational state (υ = 0) and first rotational state (J = 1). The constants obtained are: HFDFμ (D)1.826526 (7)1.818805 (5)CF (kHz)307.637 (20)158.356 (45)CH (kHz)− 71.128 (24)− 5.755 (19)SHF (kHz)28.675 (5)4.434 (9)JHF (kHz)0.529 (23)(eqQ) D354.238 (78) The electron coupled spin–spin interaction, JHF = + 530 Hz.

Determination of the structure of ArHCl

The radio frequency and microwave spectra of K = 0 states of ArHCl and ArDCl have been measured by molecular beam electric resonance spectroscopy. The rotational and hyperfine structure constants for the lowest vibrational state of the four isotopic species are ArH35 ClArD35 ClB = (B+C)/2 = 1.678511 (5)GHzB − 2DJ = 1.657596 (10)GHzDJ=20.33 (20)kHz(eqQ)aC1 = −36.250 (20)MHz(eqQ)a=−23.027(10)MHz(eqQ)aD = +102.3 (50)kHzμa=0.81144(10)Dμa=1.00355(70)D ArH37 ClArD37 ClB − 2DJ = 1.631566 (5)GHzB − 2DJ = 1.611876 (10)GHz Only the lowest vibrational state has been observed. The molecule is extremely nonrigid. The average Ar–Cl distance is 4.006 A in ArHCl and 4.025 A in ArDCl. The Ar–Cl–H angle is acute and the amplitude of the zero point angle bending is extremely large. The average Ar–Cl–H angle is near 45°, while the average Ar–Cl–D angle is near 34°. The vibrational frequency of Ar–HCl bond stretching is computed to be 32.2 cm−1 from the observed centrifugal distortion constant.

Benzene dimer: A polar molecule

The electric deflection of molecular beams of (C6H6)2, produced by adiabatic expansion, has been measured. The benzene dimer is observed to be a polar species. It is likely that the structure of this species is that of two perpendicular planes, as is observed for nearest neighbors in crystal and liquid benzene.

Internal dynamics of van der Waals complexes. I. Born–Oppenheimer separation of radial and angular motion

An efficient method has been developed for calculating ground state properties of atom–diatomic van der Waals complexes. The wide amplitude bending motion is decoupled from the radial motion in a way analogous to the Born–Oppenheimer separation of electronic and nuclear motion. The treatment furnishes rigorous upper and lower bounds to the ground state energy that are typically ±3 cm−1 for the Ar–HCl surfaces considered. Extensive comparison of this technique with the close‐coupling method of Dunker and Gordon [J. Chem. Phys. 64, 354 (1976)] using intermolecular potentials for the Ar HCl complex indicates excellent agreement in the prediction of angular expectation values and rotational constants for the ground state, while realizing an approximate 700‐fold reduction in computation time.

Molecular beam studies of benzene dimer, hexafluorobenzene dimer, and benzene–hexafluorobenzene

A detailed study of the electric deflection of molecular beams of (C6H6)2, (C6F6)2, and C6H6–C6F6 is reported. Although no resolved microwave or radio frequency transitions were observable, examination of unresolved beam transitions at radio frequencies were useful in establishing that the homomolecular dimers (C6H6)2 and (C6F6)2 are asymmetric rotors while the heteromolecular dimer C6H6–C6F6 is a symmetric top. From analysis of the quantitative electric deflection the dipole moment of C6H6–C6F6 is 0.44±0.04 D.

Energy‐Transfer Processes in Monochromatically Excited Iodine Molecules. I. Experimental Results

The fluorescence excited in iodine by the green emission line of mercury, in the presence of foreign gases, has been examined by high‐resolution photoelectric photometry. Cross sections for quenching, vibrational, and rotational energy transfer for the v′ = 25, J′ = 34 level of the B 3Π0u+ state of iodine have been obtained, for collisions with 3He, 4He, Ne, Ar, Kr, Xe, H2, O2, CO2, SO2, CH3Cl, and NH3. Emission bands have been rotationally analyzed to yield partial total cross sections for the inelastic processes. These have been corrected for multiple scattering by a computer simulation procedure.The correlation of quenching efficiency with the mass and polarizability of the collision partner, found by Brown for the quenching of the v′ = 15 level of iodine, holds for the v′ = 25 level as well. There is no contribution to quenching efficiency from a permanent electric dipole moment. The data suggest that a complex set of interactions, including electrostatic polarization, spin—orbit forces, and specific ...

Fourier transform spectra of overtone bands of HCN from 5400 to 15100 cm−1☆

Abstract The absolute intensities and vibration-rotation constants of 26 overtone and combination bands of HCN are reported. The dynamic range for the absolute intensity measurements is nearly one million to one. Absorption spectra of HCN from 5400 to 15100 cm −1 were obtained using the Fourier transform spectrometer at the Kitt Peak National Solar Observatory with optical path lengths up to 432 m. The frequencies of 1346 assigned HCN lines were used to derive vibration-rotation constants for 23 bands (14 Σ-Σ, 4 Π-Π, 4 Π-Σ, and 1 Σ-Π) of H 12 C 14 N, 3 bands (Σ-Σ) of H 13 C 14 N, and 2 bands (Σ-Σ) of H 12 C 15 N. These new band origin and rotational constant data have been combined with existing data given in the literature to derive an improved set of vibrational (ω, x , and y ) constants and rovibrational (α and γ) constants for HCN. The vibrational dependence of the centrifugal distortion constants has also been examined. One thousand thirtysix derived line areas were used to determine absolute intensities for all 28 bands. Four weak stretch-only bands were observed for the first time: the (300)-(000), the (201)-(000), the (301)-(000) and the (202)-(000). Such data should be an important aid in accurately determining the CN contribution to the potential and dipole moment functions. Finally, we present a comparison of 13 of the measured absolute overtone intensities (stretching states only) with recent ab initio results.

Intermolecular potential between an atom and a diatomic molecule: The structure of ArCIF

Author Institution: Department of Chemistry, Harvard University; Bell Laboratories, Harvard University

Centrifugal distortion in ArHCl

Measurements of centrifugal distortion constants for four isotopic species of the weakly bound, wide amplitude bender ArHCl are reported. Their relationship to an effective radial potential and the associated vibrational wavefunction is discussed. Although the stretching vibrational frequency and the resulting force constant do not have a straight forward relationship to the nonharmonic, angle averaged radial potential, an interpretation of the centrifugal distortion constant in terms of the standard deviation—or width—of the radial wavefunction is proposed. It is shown that a harmonic approximation for the standard deviation of the wavefunction accurately reflects a realistic wavefunction for a complicated potential surface. The derived constants for the four isotopic species are as follows: D0(kHz) ω (cm−1) k (mdyn/A) σ= (〈R2〉−〈R〉2)1/2(A) ArH35Cl 20.0(4) 32.4 0.0117 0.166 ArH37Cl 19.0(4) 31.9 0.0114 0.165 ArD35Cl 17.1(4) 34.4 0.0134 0.160 ArD37Cl 16.4(4) 33.7 0.0132 0.159.