Edward A. Cohen

The rotational spectrum and structure of chlorine peroxide

The products of the ClO self‐reaction have been studied in a flowing chemical reactor using submillimeter wave spectroscopy. The complete spectrum between 415 to 435 GHz has been measured as well as selected transitions in the range 285 to 415 GHz. The major products have been identified as the ClO dimer (Cl2O2) and chlorine dioxide (OClO). The observed rotational b‐type spectra of the most abundant isotopic species35 ClOO35Cl and 37ClOO35Cl have been analyzed. The observed nuclear spin statistics for the main species, the relative abundance of the lesser species, and the structure determination demonstrate unambigiously that the ClO dimer must possess identical chlorine atoms in a peroxide structure. The rotational constants as well as a complete set of quartic centrifugal distortion constants have been determined. Structural parameters for the vibronic ground state have been calculated: rOO=142.59(21) pm, rClO=170.44(4) pm, ∠ClOO=110.07(1)° and dihedral angle=81.03(1)°. Rotational transitions in the fir...

The rotational-torsional spectrum of carbodiimide: A probe for the unusual dynamics

Abstract The rotation-torsion spectrum of carbodiimide, HNCNH, a constituent of the vapor of cyanamide, H2NCN, was measured in the region from 15 GHz to 330 cm−1 using a high-resolution Fourier transform spectrometer, a laser single-sideband spectrometer, a millimeter-wave and a submillimeter-wave spectrometer. Aside from a small doublet splitting ( 1 115 (14) . This work provides an extensive high precision data base for HNCNH, making a radioastronomical search for this molecule possible.

The rotational spectrum and molecular parameters of ClO in the v=0 and v=1 states

Abstract The J = 9 2 ← 7 2 , 2 Π 3 2 and 2 Π 1 2 , ground vibrational state transitions of 35ClO and 37ClO and the 2 Π 1 2 , excited vibrational state transitions of 35ClO have been observed in the 164–167 GHz region. Additional measurements have also been made on the J = 3 2 ← 1 2 and J = 5 2 ← 3 2 transitions of both the ground and excited vibrational states. All measurements were made using millimeter oscillators which were phase locked to harmonics of a Hewlett-Packard microwave spectrometers X-band source. Λ-doubling splitting of a few 2 Π 1 2 transitions was resolved. When magnetic and nuclear quadrupole hyperfine terms off-diagonal in J and Ω in the Hunds case (a) representation were included in addition to the usual diagonal terms, an excellent fit to all of our observed transitions resulted. The most significant change from previously determined parameters is the centrifugal distortion constant D for which the values, D0 = 0.03972(26) MHz for 35ClO, D0 = 0.03888(32) MHz for 37ClO and D1 = 0.0395(21) MHz for 35ClO are obtained. Values of 1.56959(1) A for the equilibrium bond length and 854(7) cm−1 for the equilibrium vibrational frequency are derived from the measured spectra. In addition, values for the Λ-doubling constant βp and the quadrupole coupling constant eQq2 were derived from the measured spectra for the first time.

The rotation-inversion spectra and vibration-rotation interaction in NH2D

Abstract An additional 86 lines of the NH 2 D rotation-inversion spectrum were measured between 7.5 and 850 GHz. These data and the existing NH 2 D and ND 2 H data are fitted to a Hamiltonian in which the vibration-rotation interaction is included in the form of an offdiagonal inertial tensor term. For comparison with the symmetric ammonias an oblate basis and a Watson-type reduced “ S ” set of distortion constants are used. A theory for the interaction term is given which is in excellent agreement with experiment. Structural parameters are derived. The magnitude and relative sign of the two dipole moment components of NH 2 D are determined and previously measured nitrogen hyperfine structure for both species is reexamined using improved rotational wavefunctions.

The rotational spectra, molecular structure, dipole moment, and hyperfine constants of HOBr and DOBr

Abstract Pure rotational spectra of the 79Br and 81Br isotopic species of gaseous hypobromous acid, HOBr and DOBr, as well the v3 = 1 excited state of HOBr have been observed and analyzed. Structural parameters have been derived from the ground state rotational constants. The permanent molecular dipole moment of DOBr and the bromine nuclear quadrupole coupling and spin rotation constants of all the species have been determined.

The infrared and microwave spectra of ozone for the (0, 0, 0), (1, 0, 0), and (0, 0, 1) states

Abstract New measurements of the ozone spectrum in the microwave and 10-μm infrared regions have been made. These new lines have been fit to a three-state Hamiltonian model which includes Coriolis interactions beteen (0, 0, 1) and (1, 0, 0). The model requires additional Coriolis parameters, as well as an appreciation for the parameters which are indeterminate. Transition dipole moments have been derived from the intensities of selected infrared lines.

The rotational spectrum and molecular parameters of BrO in the 2Π32 state

Abstract The ν = 0 and 1 rotational spectrum of BrO in the 2 Π 3 2 state has been observed in selected regions between 60 and 400 GHz. The precision of previously measured parameters and the quality of the fit has been improved. In addition, the centrifugal distortion constant, D02, the effective Λ-doubling constant, qeff, the perpendicular quadrupole coupling constant, eqQ2, and a linear combination of the magnetic hyperfine constant, b, and nuclear spin-rotation constant, Crs, have been measured for the first time. The values of ωe and ωexe derived from the mechanical constants are in good agreement with very recent optical data.

The microwave spectrum of the AlO radical

The rotational spectrum of the aluminum monoxide radical in the ground electronic state X 2Σ+ was observed in the millimeter‐ and submillimeter‐wave region. Aluminum monoxide radicals were generated directly in a flow reactor absorption cell by the reaction of N2O with aluminum vaporized from a high‐temperature crucible. The observed spectrum was analyzed to yield molecular constants including the rotational constant, centrifugal distortion constant, spin–rotation interaction constant, magnetic hyperfine interaction constants, and nuclear quadrupole coupling constant.

The microwave spectrum of 14NH3 in the v = 000011 state

Abstract The frequencies and assignments of 50 lines in the pure inversion spectrum of 14 NH 3 in the 0001 1 vibrational state are reported in the microwave frequency region 18–53 GHz and in selected regions up to 58 GHz. The J = 0 inversion frequency, K -type doubling constant K , l = 2, −1 and molecular dipole moment in this state are 32 904.7 ± 2.0 MHz, 1.958 ± 0.040 MHz and 1.459 ± 0.002 D, respectively, where model inadequacies are included in the uncertainties of the first two parameters. The dipole moment measurements for this and the ground state are in excellent agreement with Stark laser measurements. An expression containing the effective l -type doubling constant is obtained from the combination of frequencies [ν(1, 1, 1) − ν(1, 1, −1) − ν(2, 1, 1) + ν(2, 1, −1)] 8 = 10 361.894 ± 0.004 MHz . A preliminary value for the l -type doubling constant is 10 655 ± 20 MHz.

The rotational spectrum and molecular properties of bromine dioxide, OBrO

The rotational spectrum of the OBrO radical has been observed in the gas phase over the solid products of the O+Br2 reaction. Spectra have been measured for both O79BrO and O81BrO in their (000), (010), and (020) vibrational states in selected regions between 88 and 627 GHz spanning the quantum numbers 1⩽N⩽61 and 0⩽Ka⩽14. The spectra are well described by a Hamiltonian which includes centrifugal distortion effects for fine and hyperfine terms. The molecular structure, the dipole moment, and the harmonic force field have been derived, and they, as well as fine and hyperfine structure constants, are compared with data of related molecules and electron spin resonance data from OBrO isolated in cryogenic salt matrices.