The microwave spectra of ten isotopic species of formamide (H2N–CHO) have been investigated. Type a and type b transitions have been identified and measured for all ten species. The inertial defect is found to decrease whenever a heavier isotope is substituted for any atom in the NH2 group, and in fact is negative for four of the species studied. It is concluded that the molecule is nonplanar with the H2N–C group forming a shallow pyramid. The structural parameters deduced from the rotational constants are: r(N–H′, where H′ is trans to the aldehyde hydrogen) = 1.014±0.005 A, r(N–H″, where H″ is cis to the aldehyde hydrogen) = 1.002±0.005 A, r(N–C) = 1.376±0.010 A, r(C–H) = 1.102±0.010 A, r(C=O) = 1.193±0.020 A, ∠H′NH″ = 118°53′ ±40′, ∠H″NC = 120°37′±40′, ∠H′NC = 117°9′±40′, ∠NCO = 123°48′±40′, ∠NCH = 113°14′±40′ and ∠OCH = 122°58′±40′. The dihedral angles between the H′NC plane and the NCO plane, and between the H″NC plane and the NCH plane, are 7°±5°, and 12°±5°, respectively. In all the spectra investigated each line was accompanied by a vibrational satellite line of anomalously high intensity. Measurements of relative intensities were carried out for H2N14–CHO, cis- and trans-HDN14–CHO, and D2N14–CHO. The energy levels (above the zero point) deduced from these measurements show a very large isotope shift, and are interpreted as being due to the first excited state of the NH2 wagging frequency. A pyramidal model for formamide will have two equilibrium configurations separated by a potential barrier. With a Manning type potential, a barrier of 370±50 cm−1, hindering the ``inversion-wagging'' type of motion, is determined. The equilibrium value of the normal coordinate calculated from the Manning potential is found to be in good agreement with that found in the structure determination.

The pure rotational spectrum of water vapor was measured over the frequency range 5-125 cm-I at a resolution of approximately 0.07 em-I. A complete set of energy levels up to J = 7 was derived. The groundstate rotational constants were calculated and agree well with those derived from near-infrared data. The values of the ground-state rotational constants are Ao= 27.8761±0.OO34 em-I, Bo= 14.5074±0.0090 em-I, and C o =9.2877±0.OO21 em-I. The six quartic distortion constants were also determined along with the higher-order distortion constant associated with the a axis of rotation.

The differential scattering cross section for single carbon particles is measured in the visible. The data are mathematically inverted to obtain the complex index of refraction and particle radius.

No abstract

A high-resolution, far ir lamellar grating interferometer that operates in either a single-beam or a double-beam differencing mode of operation is described. The instrument covers a frequency range of 10 cm(-1) to 125 cm(-1) (1000 micro to 80 micro). To illustrate the general performance of the instrument the pure rotational spectrum of water vapor between 15 cm(-1) and 115 cm(-1) is presented. It is estimated that the absorption line centers of strong isolated lines are measured to within +/-0.008 cm(-1). To illustrate the resolution of the instrument, low wavenumber portions of the pure rotational spectrum of DCl are shown. The Cl(35)-Cl(37) isotope splitting of the J = 2 --> 3 transition (32.3 cm(-1)) is clearly resolved. The calculated separation of these two lines is 0.094 cm(-1).