D. E. Mann

Microwave Spectra of Molecules Exhibiting Internal Rotation. I. Propylene

The microwave spectrum of propylene, CH3CH:CH2, has been investigated in the region 17–36 kmc. Measurements have been made on the normal isotopic species and on the H3CC13H:CH2 species. Most of the observed lines are split slightly as a result of internal rotation. These splittings have been satisfactorily analyzed by the methods of Hecht and Dennison, giving an internal potential barrier of 692.4±6 cm—1 or 1978±17 cal/mole. Principal moments of inertia (in units of amu A2) are 10.973, 54.312, and 62.175 for H3CCH:CH2 and 11.160, 54.318, and 62.382 for H3CC13H:CH2. The electric dipole moment has a magnitude of 0.364 D and makes an angle of 8° with the a principal axis. With reasonable assumptions concerning the location of the hydrogen atoms the remaining structural parameters are: rCC=1.488 A, rC:C=1.353 A, ≤ CCC=124°45′.

Normal Coordinate Analysis of Halogenated Ethylenes. I. General Methods

Methods and detailed algebraic expressions are given for the normal‐coordinate analysis of ethylenic molecules. In the following paper they are applied to the calculation of potential constants, normal modes, and vibrational frequencies for a series of perhalogenated ethylenes. A force field of the Urey‐Bradley type is used for the planar vibrations, and a simple valence‐type potential function is applied to the nonplanar motions. The force constants established for the molecules with Vh symmetry are to be used with only linear interpolation and no further adjustment to calculate the fundamental frequencies and modes of all the remaining, less symmetrical ethylenes. For the Vh molecules the vibrational secular equations are set up in the customary GF matrix fashion. The other ethylenes require a somewhat different form which is more readily adapted to calculation by an electronic digital computer. In order that the force constants determined for the Vh molecules be as good as possible a method is given fo...

Microwave Spectra of Molecules Exhibiting Internal Rotation. IV. Isobutane, Tertiary Butyl Fluoride, and Trimethylphospine

Several microwave transitions of (CH3)3CH, (CH3)3CF, and (CH3)3P have been measured and assigned. Rotational constants B0 for the three molecules are 7789.45, 4712.15, and 5816.24 Mc, respectively. Molecular structures and dipole moments have been determined. The (CH3)3CF structure indicates an unusually long CF bond. The prominent satellite lines have been assigned to excited vibrational states; the l‐type doubling pattern of transitions in degenerate states has been fitted to theory. Vibrational frequencies determined from relative intensity measurements agree with infrared and Raman results but indicate an incorrect species assignment in (CH3)3P. Frequencies of the torsional vibrations have been used to derive information of the potential function for internal rotation. The leading Fourier coefficient in this function is 3900, 4300, and 2600 cal/mole, respectively, for (CH3)3CH, (CH3)3CF, and (CH3)3P. The terms representing interactions among the CH3 groups are much smaller.

Microwave Spectra of Molecules Exhibiting Internal Rotation. III. Trimethylamine

The microwave spectrum of methylallene, CH3CH:C:CH2, has been investigated in the region 16–33 kmc, and the J=1→2, 2→3, and 3→4 transitions measured. Most of the observed lines are split slightly as a result of internal rotation. Analysis of the splittings by the methods of Hecht and Dennison leads to an internal potential barrier of 556.0±2 cm—1 or 1589±6 cal/mole. The principal moments of inertia (in units of amu A2) are 14.93, 120.321, and 128.713. The electric dipole moment is 0.401 D and makes an angle of 10°8′ with the a principal axis.

Infrared Spectra and the Structures and Thermodynamics of Gaseous LiO, Li2O, and Li2O2

The vapor above heated lithium oxide (Li2O) has been investigated mass spectrometrically and by infrared matrix‐isolation spectroscopy. The vapor composition and Knudsen effusion rates were measured as functions of temperature, and the matrix spectra of the principal lithium oxide species—Li2O, LiO, Li2O2—identified and analyzed for different isotopic abundances. The predominant vapor species Li72O is probably linear with r(Li–O) = 1.59 A, and has fundamentals ν1, ν2, ν3 at [760], [140], and 987 cm—1, respectively. Its heat of formation ΔH0°(f) = —43.7±2.5 kcal/mole. The diatomic molecule Li7O has ν = 745 cm—1, an estimated bond length r = 1.62 A, and ΔH0°(f) = +16.0±5 kcal/mole. The previously undetected molecule Li72O2 is shown to resemble the alkali halide dimers in having a planar rhombic (Vh) structure for which the O–Li–O angle and Li–O bond length are estimated to be 116° and 1.90 A, respectively. Its B2u and B3u frequencies are found at 324 and 522 cm—1, respectively, in a krypton matrix. The rema...

Spectroscopy of Fluorine Flames. I. Hydrogen‐Fluorine Flame and the Vibration‐Rotation Emission Spectrum of HF

The hydrogen fluoride vibration‐rotation emission spectrum from a hydrogen‐fluorine diffusion flame has been studied under high dispersion from 3200 cm−1 in the infrared to about 5500 A in the visible. Measurements were made on the rotational lines in 23 bands including (1–0), (2–1), and (3–2) of the Δv=1 sequence; (2–0), (3–1), (4–2), (5–3), and (6–4) of Δv=2; (3–0), (4–1), (5–2), and (6–3) of Δv=3; (4–0), (5–1), (6–2), (7–3), (8–4), and (9–5) of Δv=4; and (5–0), (6–1), (7–2), (8–3), and (9–4) of Δv=5. Complete rotational and vibrational analyses were carried out. The constants Bv, Dv, and Hv are given for v=0 to 9. The data were extensive and precise enough to warrant an extended Dunham treatment from which 18 coefficients could be determined, including those for terms in (v+½)5 and J4(J+1)4. Band centers for 22 bands and the vibrational term values Ev for v=0 to 9 are given.

Matrix-isolation study of the reaction of f atoms with co - infrared and ultraviolet spectra of the free radical fco.

FCO has been obtained in a CO and in an Ar matrix at 4°, 14°, and 20°K by the reaction with CO of F atoms produced upon photolysis of OF2, of NF2, or of t‐N2F2, as well as by the photolysis of F2CO or of HFCO. The three vibrational fundamentals of the free radical FCO appear at 1855, 1018, and 626 cm−1. Experiments employing 13C16O and 12C18O confirm the infrared identification of FCO. In ultraviolet‐absorption studies on matrix‐isolated FCO an extensive series of bands has been observed between 2200 and 3400 A. The most prominent progression in this system involves bands spaced at approximately 650‐cm−1 intervals. It is likely that this progression is associated with the upper‐state bending mode of FCO. F2CO and (FCO)2 are also produced in the reaction of F atoms with a CO matrix, and features of their infrared spectra are reported. A supplementary observation of the ultraviolet‐absorption spectrum of gaseous F2CO shows a band system between 1800 and 2100 A, with spacings of approximately 1700 cm−1. Presumably this system is contributed by the n→π* carbonyl transition. The approximate geometric structure and the nature of the chemical bonds of FCO are discussed, and the mechanisms of formation of this species and of the other observed products are considered. An estimate of the thermodynamic properties of FCO is given.

Microwave Spectrum and Structure of Sulfuryl Fluoride

The microwave spectrum of sulfuryl fluoride, SO2F2, has been reinvestigated. The spectra of the S32 and S34 species in natural abundance have been analyzed, and the structure has been determined with the aid of the S34 isotope shift. The correction for zero‐point vibration was shown to be small. The structural parameters are: rSO=1.405±0.003 A, rSF=1.530±0.003 A, <OSO=123°58′±12′, and <FSF=96°7′±10′. The molecular dipole moment is 1.110±0.015 Debye units. A number of satellite lines were observed and assigned to excited vibrational states. Some anomalies in the measured rotational constants for the excited states have been interpreted in terms of a Coriolis‐type interaction between the fundamentals ν4(A1) and ν5(A2). From an analysis of this interaction the frequency of the hitherto unobserved ν4(A1) fundamental was found to be 388±15 cm—1.

Normal Coordinate Analysis of Halogenated Ethylenes. II. Perhalogenated Ethylenes

The methods described in the preceding paper have been applied to the normal coordinate analysis of the fundamental vibrations of 27 perhalogenated ethylenes which contain F, Cl, or Br. Force constants for the planar modes of the key molecules, C2F4, C2Cl4, and C2Br4, have been obtained by an adjustment procedure based on the method of least squares. The agreement between the calculated and observed fundamentals is quite good. The constants established for the key molecules were then used, either directly or with a simple interpolation scheme, to calculate the fundamentals of the remaining 24 ethylenes. Comparisons with experimental results have been made where possible and indicate good agreement for the out‐of‐plane as well as inplane vibrations. The planar normal modes of C2F4, C2Cl4, and the 5 fluorochloroethylenes are depicted.

Microwave Structure Determinations on Tertiary Butyl Acetylene and Tertiary Butyl Cyanide

The microwave spectra of eight isotopic species of tertiary butyl acetylene and four isotopic species of tertiary butyl cyanide have been measured and analysed. Some transitions in excited vibrational states have been assigned. Measurements of the Stark effect lead to a dipole moment of 0.661±0.004 D for (CH3)3CCCH and 3.95±0.05 D for (CH3)3CCN. From the isotope shifts in the moments of inertia the following bond distances (rs) are obtained: r(C≡C) = 1.209±0.001 A and r(≡C–H) = 1.056±0.001 A in (CH3)3CCCH; r(C≡N) = 1.159±0.001 A in (CH3)3CCN. The tertiary butyl group appears to have very nearly the same dimensions in these two compounds as in (CH3)3CH and (CH3)3CF. The tertiary carbon atom cannot be located with high precision, but the best estimates lead to a C–C≡ distance of 1.495±0.015 A in both (CH3)3CCCH and (CH3)3CCN. This is 0.02–0.04 A longer than the normal value for this distance. There appears to be a consistent tendency for the (CH3)3C— group to lengthen the adjacent bond, but it is difficult ...