Stewart E. Novick

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.

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.

Hydrogen bonding: The structure of HF–HCl

The structure of the hydrogen bonded complex formed between HF and HCl has been determined by molecular beam electric resonance spectroscopy. The molecule HF–HC1 is a slightly asymmetric prolate top. The spectroscopic constants determined from K=0 spectra of several isotopic species are 〈eqQDa〉 for HF D35Cl is 146(15) kHz. The equilibrium atomic arrangement is HF–HCl with the internal proton colinear with the two heavy atoms spaced 2.12 A from the fluorine atom. The exterior proton is off axis by 50°. The bonding of this complex is discussed with respect to other gas phase complexes and hydrogen halide crystal structures. It appears that a model which involves electron donation from the highest occupied molecular orbital (HOMO), of one submolecule to the lowest unoccupied molecular orbital (LUMO) of the other gives a useful qualitative description of complex formation between closed shell species.

Molecular beam electric resonance spectroscopy of the nitric oxide dimer

Microwave and radiofrequency spectra have been observed for (NO)2 using the technique of molecular beam electric resonance spectroscopy. Precise values have been determined for rotational, nuclear quadrupole coupling and spin-rotation constants of the ground electronic state treated as a singlet state. The values obtained are A = 25829·4803(20) MHz, B = 5614·3093(4) MHz, C = 4605·4396(12) MHz xaa = -4·0652(2) MHz, xbb - xcc = -8·5498(6) MHz caa = 10·4(5) kHz, cbb = 13·8(4) kHz, ccc = 0·8(4) kHz. The electric dipole moment has also been determined: μ = 0·17120(2) D. From these data (NO)2 is interpreted to have a symmetric cis-planar structure with the structural parameters r NN = 2·33(12) A, r NO = 1·15(1) A, ∠NNO = 95(5), 1/2(r NN + r NO) = 2·444(8) A. The quadrupole coupling constants of the nitrogen nuclei and the dipole moment demonstrate that little electron rearrangement occurs on dimer formation. In addition xaa and xbb - xcc indicate that the unpaired π electrons lie in the plane of the dimer imply...

Determination of the structure of ArHF

Radio‐frequency and microwave spectra of K = 0 states of ArHF in the ground vibrational state have been measured by molecular beam electric resonance spectroscopy. The rotational constant is (B+C)/2=3065.719 MHz; the component of the dipole moment along the a inertial axis is μa = 1.332 D. From the centrifugal distortion constant, DJ = 72.1 kHz, the stretching frequency of the van der Waals bond is estimated to be 42.1 cm−1. In analogy with ArHCl the internal Ar–F–H angle θ is expected to be acute and the average value of the angle is 48.20°. The equilibrium configuration is likely to be near linear with atomic arrangement ArHF. The vibrationally averaged Ar–F distance is 3.540 A.

Intermolecular potential between an atom and a linear molecule: The structure of ArOCS

The radio frequency and microwave spectrum of ArOCS has been measured by molecular beam electric resonance spectroscopy. ArOCS is a prolate, slightly asymmetric top. The rotational constants and dipole moment components of the ground vibrational state are as follows: A = 6786.014(20) MHz, B = 1509.909(6) MHz, C = 1227.220(6) MHz, μa = 0.2146(10) D, μb = 0.669(2) D. The complex has a nonlinear, T‐shaped structure and the vibrationally averaged distances are Ar–C = 3.578(1), Ar–O = 3.601(1), and Ar–S = 4.101 A. The observed structure is analogous to isoelectronic and isovalent chemically bound systems, and it is shown to be that expected from an interaction of the highest occupied orbital of Ar with the lowest unoccupied orbital of OCS.

Laser photoelectron, photodetachment, and photodestruction spectra of O−3

Fixed frequency laser photoelectron spectrometry and variable frequency laser photodetachment and photodestruction spectroscopy of the ozonide ion, O−3, have been accomplished. The electron affinity of ozone is measured to be EA(O3) =2.1028(25) eV, in good agreement with previous measurements of less accuracy. Progressions in the spectra are analyzed to yield the symmetric stretching frequency and the bending frequency of the ozonide ion to be 982(30) and 550(50) cm−1, respectively. While no evidence is found for a long lived excited electronic state of O−3, an excited electronic state of neutral ozone is found roughly 0.7–1.1 eV above the ground state. Models for the dissociation of O3− are examined to explain why the photoelectron and photodetachment spectra fail to show a strong progression in the symmetric bending vibrational mode. Attempts to measure the electron affinity of CO−3 were unsuccessful. Limits placed by this attempt and our EA(O3) value are invoked in a discussion of some recent disagreem...

HFClF: Structure and bonding

The structure of the complex formed between HF and ClF has been determined by molecular beam electric resonance spectroscopy. The molecule HFClF is a slightly asymmetric prolate top. The spectroscopic constants determined from K=0 spectra of several isotopic species are as follows: The atomic arrangement in the complex is HFClF with the three heavy atoms collinear. The proton is off axis by 55°. The FCl van der Waals bond length is 2.76 A. Comparison of the structure of HFClF with that of (HF)2 shows striking similarities. It appears that the bonding in both complexes is quite similar.