CNC Bending Research Articles

The low- J rotational spectrum of methyl isoselenocyanate

The microwave spectrum of methyl isoselenocyanate, CH 3NCSe, has been measured in the region 6–10 GHz using a microwave Fourier-transform spectrometer. For the most abundant isotopic species, with 80Se, the a-type J + 1 ← J rotational transitions ( J = 1 and 2) have been assigned for the ground and several excited states of the CNC bending mode ν 10. The observed spectrum has been analyzed using the quasisymmetric top model. The shape of the CNC bending potential function has been determined in the least-squares fitting to the rotational transitions arising from molecules in states of the ν 10 mode with v 10 ranging from 0 to 4. The potential function is calculated to be strongly anharmonic, with a minimum at the CNC angle of 161.3° and a barrier to linearity of the CNCSe skeleton of only 24 cm −1. The effective barrier to internal rotation of the methyl group is estimated to be 1.8 cm −1. The microwave spectra of different isotopic species have been predicted and rotational transitions for the CH 3NC 78Se isotopomer have been assigned.

Three kinds of case-based learning in sheet metal manufacturing

The paper outlines three applications of case-based learning in sheet metal manufacturing by utilization of artificial intelligence, each based on different concepts. One topic is the synthesis with feature processing for the process outline on a CNC bending machine. Statistics on fail and success influence weights of rules in an expert system. Another example is the classification of sheet metal parts. Real objects and their components are represented by a frame like data structure, which is embedded in a semantic network. Grouping of work pieces is done by a decision method of Bayes. This method is also used for part diagnosis to avoid possible defects of tools and machines.

ChemInform Abstract: The Microwave Spectrum of Methyl Isoselenocyanate: CH3NCSe as a Quasi‐Symmetric Top.

Abstract The microwave spectrum of methyl isoselenocyanate, CH3NCSe, has been measured in the region 18–40 GHz. The a-type J + 1 ← J rotational transitions (J = 5 to 10) in the ground vibrational state of the molecule have been assigned for the three isotopic species with 82Se, 80Se, and 78Se. For the most abundant isotopic species, with 80Se, the rotational transitions in the excited states of the CNC bending mode v10 = 1 and 2 have also been assigned. Contrary to the previous investigation [T. Sakaizumi et al., Bull. Chem. Soc. Japan 59, 1614–1616 (1986)], it has been shown that the observed spectrum is consistent with that of a quasi-symmetric top molecule. The rotation-vibration constants have been determined, showing an unusual variation with excitation of the CNC bending mode. The CNC bending potential function has been determined in preliminary calculations using a quasi-symmetric top model. The potential function is calculated to be very anharmonic, with an equilibrium CNC angle of about 162° and a barrier to linearity of the CNCSe skeleton of about 25 cm−1. From accidental resonances observed for the ground state transitions the barrier to internal rotation of the methyl group was estimated to be about 3 cm−1.

The microwave spectrum of methyl isoselenocyanate: CH 3NCSe as a quasi-symmetric top

The microwave spectrum of methyl isoselenocyanate, CH 3NCSe, has been measured in the region 18–40 GHz. The a-type J + 1 ← J rotational transitions ( J = 5 to 10) in the ground vibrational state of the molecule have been assigned for the three isotopic species with 82Se, 80Se, and 78Se. For the most abundant isotopic species, with 80Se, the rotational transitions in the excited states of the CNC bending mode v 10 = 1 and 2 have also been assigned. Contrary to the previous investigation [T. Sakaizumi et al., Bull. Chem. Soc. Japan 59, 1614–1616 (1986)], it has been shown that the observed spectrum is consistent with that of a quasi-symmetric top molecule. The rotation-vibration constants have been determined, showing an unusual variation with excitation of the CNC bending mode. The CNC bending potential function has been determined in preliminary calculations using a quasi-symmetric top model. The potential function is calculated to be very anharmonic, with an equilibrium CNC angle of about 162° and a barrier to linearity of the CNCSe skeleton of about 25 cm −1. From accidental resonances observed for the ground state transitions the barrier to internal rotation of the methyl group was estimated to be about 3 cm −1.

ChemInform Abstract: Electric Dipole Moment Functions of CH3NCO and CH3NCS.

Abstract The Stark effect of some rotational transitions of two quasi-symmetric top molecules, namely methyl isocyanate (CH3NCO) and methyl isothiocyanate (CH3NCS), has been investigated and analyzed in terms of a five-dimensional quasi-symmetric top model. The electric dipole moment is expressed as a function of coordinates of the large-amplitude motions: the CNC bending and internal rotation. The function parameters have been determined using the experimental data combined with the results of ab initio SCF calculations. The effective electric dipole moments of both molecules have been estimated for the ground and excited CNC bending states.

Electric dipole moment functions of CH 3NCO and CH 3NCS

The Stark effect of some rotational transitions of two quasi-symmetric top molecules, namely methyl isocyanate (CH 3NCO) and methyl isothiocyanate (CH 3NCS), has been investigated and analyzed in terms of a five-dimensional quasi-symmetric top model. The electric dipole moment is expressed as a function of coordinates of the large-amplitude motions: the CNC bending and internal rotation. The function parameters have been determined using the experimental data combined with the results of ab initio SCF calculations. The effective electric dipole moments of both molecules have been estimated for the ground and excited CNC bending states.

The microwave spectrum of methyl isothiocyanate

Abstract The microwave spectrum of methyl isothiocyanate, CH 3 NCS, has been measured in the range from 5 to 26 GHz. Almost 300 lines have been assigned to the a -type J + 1 ← J rotational transitions ( J = 0 to 4) arising from molecules in the ground state and excited torsional and CNC bending states. The observed spectrum has been analyzed and successfully interpreted in terms of the five-dimensional quasi-symmetric top molecule model accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. In the least-squares fitting to the observed transition energies the values of the parameters of the CNC bending-torsional potential function have been determined.

The microwave spectrum of methyl isocyanate

The microwave spectrum of methyl isocyanate, CH 3NCO, has been measured in the range from 8 to 40 GHz. More than 200 lines have been assigned to the a-type J + 1 ← J rotational transitions ( J = 0 to 3) arising from molecules in the ground state and excited torsional and CNC bending states. The observed spectrum has been analyzed and successfully interpreted in terms of the five-dimensional quasi-symmetric top molecule model accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. In the least-squares fitting to the observed transition energies the values of the parameters of the CNC bending-torsional potential function have been determined.

Methyl isocyanate: An analysis of the low- J rotational spectrum using the quasi-symmetric top molecule approach

The low- J rotational spectrum of methyl isocyanate (CH 3NCO) has been analyzed in terms of the quasi-symmetric top molecule model, accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. An assignment of 25 J = 1 ← 0 and 2 ← 1 rotational transitions arising from the various CNC bending and torsional states is proposed. The molecule is found to be a nearly freely internally rotating quasi-symmetric top, with a barrier to linearity of the CNCO skeleton of 1049 cm −1 and an equilibrium CNC valence angle of 140.2°.

ChemInform Abstract: MICROWAVE SPECTRA OF CIS AND TRANS 2‐FURYLISOCYANATE CONFORMERS

Abstract The microwave spectrum of 2-furylisocyanate has been obtained in the frequency region from 8 to 40 GHz. This spectrum is attributed to the ground state of the cis and trans configurations. The rotational constants for both ground vibrational states have been determined. Two sets of vibrational satellites are observed and assigned to the modes of C-N torsion and CNC bending. The microwave results show and MINDO/3 calculations confirm that the barrier between the cis and trans conformers is high and that the cis conformer is more stable than the trans by 3 kcal mol −1 .

Microwave spectra of cis and trans 2-furylisocyanate conformers

The microwave spectrum of 2-furylisocyanate has been obtained in the frequency region from 8 to 40 GHz. This spectrum is attributed to the ground state of the cis and trans configurations. The rotational constants for both ground vibrational states have been determined. Two sets of vibrational satellites are observed and assigned to the modes of C-N torsion and CNC bending. The microwave results show and MINDO/3 calculations confirm that the barrier between the cis and trans conformers is high and that the cis conformer is more stable than the trans by 3 kcal mol −1.

CNC bending improves exhaust pipe performance

CNC bending improves exhaust pipe performance

ChemInform Abstract: MICROWAVE SPECTRUM OF ETHYL ISOTHIOCYANATE

The microwave spectrum of ethyl isothiocyanate, CH3CH2NCS, has been obtained in the frequency region from 8.5 to 35 GHz. The spectrum identified is attributed to the cis configuration, namely, the methyl group eclipses the isothiocyanato group. The rotational constants for the ground vibrational state obtained are A=1419±10, B=1799.27±0.02 and C=1612.14±0.02 MHz. The dipole moment of this rotamer is μtotal=3.33±0.03 D (μa=3.33±0.03 D, μb=0.07±0.02 D). Two sets of vibrational satellites were observed and assigned to the modes of C–N torsion (58±30 cm−1) and CNC bending (107±30 cm−1).

Microwave Spectrum of Ethyl Isothiocyanate

Abstract The microwave spectrum of ethyl isothiocyanate, CH3CH2NCS, has been obtained in the frequency region from 8.5 to 35 GHz. The spectrum identified is attributed to the cis configuration, namely, the methyl group eclipses the isothiocyanato group. The rotational constants for the ground vibrational state obtained are A=1419±10, B=1799.27±0.02 and C=1612.14±0.02 MHz. The dipole moment of this rotamer is μtotal=3.33±0.03 D (μa=3.33±0.03 D, μb=0.07±0.02 D). Two sets of vibrational satellites were observed and assigned to the modes of C–N torsion (58±30 cm−1) and CNC bending (107±30 cm−1).

Microwave Spectrum, Barrier to Internal Rotation, 14N Nuclear Quadrupole Interaction, and Normal-Coordinate Analysis in Methylisocyanate, Methylisothiocyanate, and Methylthiocyanate

The microwave spectra of methylthiocyanate, methylisocyanate, and methylisothiocyanate have been re-examined under high resolution. The rotational constants of methylthiocyanate are A = 15 703.0±2.0 MHz, B = 4155.59±0.1 MHz, and C = 3354.16±0.1 MHz. The barrier to internal rotation of the methyl group determined from the Q-branch splittings in the v = 0 torsional state is 1600±80 cal/mole. Analysis of the 14N quadrupole splitting yields the following coupling constants: χaa = −3.13±0.05 MHz, χbb = 2.19±0.05 MHz, χcc = 0.94±0.05 MHz. The barrier to internal rotation in methylisocyanate is found to be 83±15 cal/mole from the splitting of the K = 0, m = ±3 lines, and χaa is 2.86±0.03 MHz. The corresponding parameters in methylisothiocyanate are found to be 304±50 cal/mole and 1.90±0.03 MHz. The microwave data are consistent with a CNC angle of 147°—148° in methylisothiocyanate as opposed to 140° in methylisocyanate and indicates C–N bond lengths in these compounds of 1.43–1.45 Å. The observed spectra of methylisocyanate and methylisothiocyanate cannot be fit by the usual semirigid internal-rotation treatment. A reasonable fit of the K = 0 lines is obtained only if a semiempirical nonrigid correction factor of the form CTm2 is used and, in addition, the methyl symmetry axis is tilted ∼3° toward the lone-pair electrons on the nitrogen atom. Calculations based on a model which includes the effects of the CNC bending motion on the over-all and internal rotation failed to improve the fit. It is concluded that an extensive vibration-rotation-interaction treatment is necessary in order to achieve a quantitative fit of the microwave data. A normal-coordinate analysis of the three molecules studied was carried out using a valence force field. The present vibrational assignment in methylthiocyanate is substantiated, and the lowest-frequency mode is found to contain a large contribution from the S–C≡N bend in addition to the CSC bend. The lowest-frequency modes in methylisocyanate and methylisothiocyanate are likewise not pure CNC bends, and the CNC bending frequencies in both molecules must be lower than presently assigned.