A.M. Mirri

General Force Field of NF3, PF3, and AsF3 by the Combined Use of Vibrational Frequencies, Centrifugal Stretching, and Coriolis Coupling Constants

Possible sources of the discrepancies between zeta parameters and centrifugal distortion constants found in the attempt to determine the general force field of NF3, PF3, and AsF3 have been analyzed. Large anharmonicities on the ν2 bending modes cannot be responsible for the results obtained by other authors; the discrepancies become smaller only by assuming that the ν4 bending modes are considerably anharmonic. On the other hand, for smaller values of the bond angle in the case of PF3 and AsF3 it is possible to obtain consistency between infrared and microwave data. For a bond angle of 98° for PF3, in agreement with recent results of electron diffraction measurements, it is possible to determine a force field which gives zeta parameters and centrifugal distortion constants within their experimental accuracy even by using anharmonic vibrational frequencies. Consistency between infrared and microwave data for AsF3 is obtained for ∠FAsF=99°±1°. In the case of NF3 the structure is very accurately known and a ...

Microwave spectrum, structure and electric quadrupole coupling constants of HOCl

Abstract The rotational “a” type spectra of H 16 O 35 Cl, H 16 O 37 Cl, D 16 O 35 Cl, D 16 O 37 Cl and D 18 O 35 Cl have been measured. The rotational constants B and C and the quadrupole coupling constants χ aa and χ bb were obtained for each isotopic species. The values of D J and D JK for H 16 O 35 Cl were also determined from centrifugal distortion analysis of the spectrum. The following values of the structural parameters were obtained: r OH = 0.959 ± 0.005 A from I a and I b , r OH = 0.975 ± 0.003 A from I b and I c , r OCl = 1.689 5 ± 0.003 5 A and

Internal rotation barrier and dipole moment of phenylsilane by microwave spectroscopy

Abstract The microwave rotational spectrum of phenylsilane has been investigated in the region from 8 to 27 GHz. From the m = 0 lines (a-type transitions) the rotational constant A ′ (less silyl top) = 5702.96, B = 1499.574, C = 1187.118 MHz and the dipole moment μ = 0.845 have been determined. From the wide splitting of the lines | m | = 3, | K | = 1 the potential barrier has been derived as V 6 = 17.78 cal/mole.

Millimeter wave spectra of NOCl and NOBr and force constant determination

Abstract First order centrifugal distortion constants of NO35Cl and NO37Cl and of NO79Br have been obtained from millimeter wave rotational spectra. Their values in KHz are: DJ = 6·35 ± 0·2 DJK = −58·5 ± 2 for NO35Cl DJ = 6·01 ± 0·2 DJK = −57·4 ± 2 for NO37Cl DJ = 3·05 ± 0·1 DJK = −54·8 ± 2 for NO79Br Using microwave and infra-red data all the force constants of the general force field have been determined for both molecules.

Millimeter Wave Spectrum and Molecular Force Field of Tetratomic C2υ Molecules: NO2F

The millimeter rotational spectrum of NO2F has been measured in the frequency range 90–200 kMc/sec. By centrifugal distortion analysis, based on the Kivelson and Wilson first‐order perturbation treatment, the following values of the ground‐state parameters were obtained: A = 13 201.31 B = 11 446.25 C = 6118.99 τaaaa = − 0.039814 τbbbb = − 0.078638 τaabb = 0.012452 τabab = −0.048868. Two different methods were used in order to determine the general quadratic force field, by combination of infrared and microwave data. The first method is based on the complete consistency between force constants and vibration frequencies of the normal species and on the best fit of the rotational spectrum. The second method uses the least‐square determination of the corrections on some starting set of force constants. All the isotopic‐ and normal‐species vibration frequencies measured by Bernitt, Miller, and Hisatsune and all the centrifugal distortion contributions on millimetric rotational transitions were used as experime...

Rotational spectrum of ONCl in the (0, 0, 1) and (0, 1, 0) vibrational states and “b” type spectrum in the ground state. Comparison of force field obtained by different combinations of experimental data

Abstract From the rotational spectrum of ONCl in (0, 0, 1) and (0, 1, 0) excited vibrational states the inertia defects in these states have been determined. The “b” type rotational spectrum in the ground state has also been measured allowing the determination of Δ0 and of all the first-order centrifugal distortion constants. It is shown that by using differences of inertia defects Δ2 and Δ3 together with centrifugal distortion constants which do not involve the planarity relations and with harmonic vibrational frequencies of two isotopic species, the harmonic vibrational frequencies of two other isotopic species can be satisfactorily predicted. By using only inertia defects differences Δ2 and Δ3 as extra data, a definite choice can be made among the three sets of force constants which equally well reproduce the harmonic frequencies of four isotopic species.

Microwave spectrum, barrier to internal rotation and dipole moment in 5-methyl-pyrimidine

Abstract The microwave rotational spectrum of 5-methyl-pyrimidine has been investigated in the region from 8 to 27 GHz, the three types of lines to be expected for a molecule of this symmetry and with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m = 0; | m | ≠ 0,3; | m | = 3 n . From the m = 0 (a-type transitions) the rotational constants A ′ (less methyl top) = 6108.41, B = 2642.198, C = 1844.196 MHz and the dipole moment μ = 2.881D have been determined. From the wide splitting of the lines | m | = 3, | k | = 1 the potential barrier has been derived as V 6 = 11.73 cal/mole.

Higher-order centrifugal distortion effects in ONCl

Abstract One hundred and nine new rotational transitions of ONCl in the ground vibrational state have been measured. A centrifugal distortion analysis of these transitions yields the values of six sextic and one octic centrifugal distortion constants. A comparison between experimental and calculated sextic distortion constants is reported.

Anharmonic force field of ONCl and ONBr by combination of infrared and microwave data

Abstract From the analysis of the microwave spectra of ON 35 Cl and ON 81 Br in several vibrational excited states, vibro-rotational constants corresponding to the ν 2 and ν 3 vibrational modes have been determined for both molecules. In order to extract information on the anharmonic force field from these experimental data and anharmonicity x ij constants obtained by other authors, the semiempirical potential function suggested by Pliva has been used. A good agreement between experimental and calculated molecular constants for both nitrosyl halides was obtained by least squares calculations using a NX , b NX , c NX , b NO , c NO , b ϕ , c ϕ Plivas parameters as variables for different values of a NO . Cubic and quartic force constants in internal displacement coordinates were derived. A comparison of the cubic constants with a constrained cubic GVFF was also carried out.

General force field of NSF from microwave and infra-red data

Abstract The analysis of centrifugal distortion in the rotational spectrum of NSF has been carried out. The following values for rotational and first order centrifugal distortion constants were obtained (Mc/s): A = 49719·48 B = 8712·34 C = 7393·12 τ aaaa = −8·796621 τ bbbb = −0·057700 τ aabb = 0·437754 τ abab = −0·089814 By combining infra-red and microwave data the following force constants were derived: T001 . 3 F 11 = 10·709 F 22 = 2·871 F 33 = 0·978 F 12 = 0·095 F 13 = −0·064 F 23 = 0·031 where F 11 , F 22 and F 12 are in mdyn/A, F 33 in mdyn.A, F 13 and F 23 in mdyn. The internal co-ordinates used are: S 1 = δ(NS), S 2 = δ(SF), S 3 = δα