Microwave spectrum of ketene

A new Stark-modulated submillimeter-wave spectrometer is described. This spectrometer has been used to analyze the microwave spectrum of three isotopomers (heavy atoms) of ketene. The rotational constants determined have been used to calculate the structure of ketene using a variety of methods. The question of planarity of ketene is also addressed. High-resolution microwave measurements have been used to determine the spin-rotation interaction in CH₂¹³CO.     

Microwave spectrum of tropone

The microwave spectrum of tropone (2,4,6-cycloheptatriene-1-one) has been obtained and assigned. The observation of a statistical weight intensity alternation indicates that the molecule has C_2v symmetry. Relative intensity measurements show the molecule to possess a low wavenumber vibration whose 1-0 interval is 60 ± 20 cm^?1. The dipole moment is found to be 4.1 ± 0.3 D by the “rate-of-growth” method.     

Microwave spectrum of DNO

The microwave spectrum of deuterated nitroxyl DNO has been observed and analyzed. The molecule was produced by the reaction of D with NO in a flow system. Both a-type and b-type transitions have been observed and the resulting rotational constants, A = 315450.3 ± 4.8 MHz, B = 38731.5 ± 1.5 MHz, and C = 34354.0 ± 1.5 MHz, are in good agreement with those of the lower electronic state ¹A′ for the electronic transition of DNO observed by Dalby. The quadrupole coupling constants for nitrogen are χ_aa = 1.03 ± 0.40 MHz, χ_bb = −6.13 ± 0.26 MHz, χ_cc = 5.10 ± 0.26 MHz. The components of the electric dipole moment of DNO have been determined to be μ_a = 1.18 ± 0.04 D and μ_b = 1.22 ± 0.04 D, giving a total dipole moment μ_total = 1.70 ± 0.05 D. The half lifetime of the molecule varies from 1 to 40 sec, depending on the condition of the surfaces of the absorption cell, which is much longer than the values reported previously.     

Microwave spectrum of dimethyldichlorosilane

The microwave spectrum of dimethyldichlorosilane has been observed and the rotational constants and centrifugal distortion constants have been determined for ³⁵Cl₂ and ³⁵Cl³⁷Cl species. From these constants, the molecular structure is determined as $\text{r(}\text{SiCl}\text{) = 2.055 ± 0.003}\text{A}\text{?}$, $\text{r(}\text{SiC}\text{) = 1.845 ± 0.005}\text{A}\text{?}$, ∠ClSiCl = 107.2 ± 0.3°, ∠CSiC = 114.7 ± 0.3°. An analysis of the ³⁵Cl₂ quadrupole splittings leads to quadrupole coupling constants of χ_aa = ?19.6 ± 0.3 MHz, χ_bb = ?3.7 ± 1.4 MHz, χ_cc = 23.3 ± 1.4 MHz, χ_bond = ?38.0 ± 1.6 MHz, and η_bond = 0.22 ± 0.08.     

Microwave spectrum of 2-aminopyridine

The microwave spectra of 2-aminopyridine-NH₂, -ND₂, and of both of the two possible -NHD molecules have been observed and assigned in the 0⁺ vibrational state of the amino group inversion vibration; the assignment for three of the molecules in the 0⁻ state is also made. From intensity measurements the 0⁺-0⁻ splitting is estimated to be 135 ± 25 cm⁻¹ for the -NH₂ molecule and 95 ± 30 cm⁻¹ for the -ND₂ molecule. The rotational constants are interpreted in terms of a structure in which the amino group is bent about 32° out of the molecular plane, the c coordinates of the two amino H atoms being 0.21 and 0.28 Å. Stark effect measurements give a dipole moment of about 0.9 D which is almost entirely in the b axis, and which changes quite significantly between the 0⁺ and 0⁻ states.     

Microwave spectrum of NF2

About 350 lines in the microwave spectrum of NF₂ have been measured in various ranges of frequency between 13.0 and 65.2 GHz by using two types of Zeeman effect spectrometers. Complete assignment of all lines has been achieved and, via the general microwave computer program SPINRO, the rotational constants, centrifugal distortion constants, dipole moment, electronic spin-rotation coupling constants, the constants for the coupling of the several nuclear spins with the electron spin and the nitrogen quadrupole coupling constants have all been obtained.By drawing upon the observed vibrational frequencies the average geometry of NF₂ has been evaluated. Force constants and Coriolis coupling constants have also been derived.The values of the spin coupling constants for N and for F indicate that NF₂ is a π-radical with the spin density mainly located on nitrogen. The multiplet patterns indicate that the ground electronic state wavefunction is antisymmetric to rotation about the molecular symmetry axis and so, for a π-radical, identifies the ground state as ²B₁ as has previously been assumed for this molecule.     

Microwave spectrum of 3-iodopropene

The microwave spectra of 3-iodopropene were measured in the frequency region 12–18 GHz. The a-type R-branch and the b-type Q-branch rotational transitions of one conformer, skew, have been assigned and the rotational constants of the ground state have been obtained: A = 17 644.34, B = 1588.12, and C = 1538.64 MHz. The second-order quadrupole effects give rise to anomalous hyperfine splittings and are analyzed by taking into account χ_ab of the quadrupole coupling tensor. The nuclear quadrupole coupling constants have been determined to be χ_aa = ?1337, χ_bb = 387, χ_cc = 950, and ∥χ_ab∥ = 1081 MHz.     

Microwave spectrum of γ-valerolactone

An Ar⁺ laser at 4579 Å is used to excite the B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li⁷Li molecule in a crossed heat pipe oven. The spectrum in the region 4400–6300 Å is recorded photoelectrically with an emphasis on the observation of higher vibrational levels in the ground state close to the dissociation limit. P and R doublets corresponding to v″ ≤ 26 originating from the (v′ = 13, J′ = 19) level are observed and identified using mass-reduced quantum numbers. Two additional ⁶Li⁷Li series, known from earlier work of Velasco, Ottinger, and Zare, are also analyzed. These data are used to construct effective Rydberg-Klein-Rees (RKR) potentials for specific J″ (=9, 19) quantum numbers of the ground state and from them the true (rotationless) potential energy curve (for X¹Σ_g⁺) is derived. This extends the previously known curve of Li₂ from 4.28 to 5.18 Å (outer turning point); this turning point corresponds to an energy which is approximately 88% of the dissociation energy, which is estimated here to be 8516 ± 18 cm^?1.     

Microwave spectrum of fluoroacetyl chloride

The microwave spectrum of fluoroacetyl chloride has been studied in the 8–40 GHz region and transitions arising from one conformer have been assigned. This conformer has all the heavy atoms in a plane with the fluorine and chlorine atoms trans to one another. The rotational constants and nuclear quadrupole coupling constants for the ground vibrational state are (in MHz): H₂FCCO³⁵Cl: A = 9025.82, B = 2403.92, C = 1920.70, χ_aa = ?47.7, χ_bb = 23,7, χ_cc = 24.1; H₂FCCO³⁷Cl: A = 8994.95, B = 2342.24, C = 1879.75, χ_aa = ?38.0, χ_bb = 18.9, χ_cc = 19.1. The spectrum of the first excited torsional state has been assigned. Some lines possibly due to a second conformer have been observed but not yet assigned.     

Microwave spectrum of 1,2-propanediol

The microwave spectrum of the sugar alcohol 1,2-propanediol (CH₃CHOHCH₂OH) has been measured over the frequency range 6.5–25.0 GHz with several pulsed-beam Fourier-transform microwave spectrometers. Seven conformers of 1,2-propanediol have been assigned and ab initio electronic structure calculations of the 10 lowest energy forms have been calculated. Stark effect measurements were carried out on several of the lowest energy conformers to provide accurate determinations of the dipole moment components and assist in conformer assignment.     

Microwave spectrum of 3-cyanocyclopropene

Microwave measurements of the normal isotopic species of 3-cyanocyclopropene have given the following ground vibrational state rotational constants: A = 19876.036 ± 0.006, B = 3533.743 ± 0.001, and C = 3417.839 ± 0.001 MHz. The value of the ¹⁴N quadrupole coupling constant χ_cc was found to be 1.62 ± 0.05 MHz, and the molecular dipole moment had a value of μ_T = 4.47 ± 0.04 Debye. The results are compared to those for related molecules, and are discussed qualitatively with respect to the molecular structure.     

Microwave spectrum of 3-methoxypropionitrile

The microwave spectrum of 3-methoxypropionitrile, CH₃OCH₂CH₂CN, has been investigated in the region 16 to 40 GHz. The spectrum reveals the presence of only one rotational isomer, the fully-trans form (with C₈ symmetry). For the ground vibrational state the rotational constants are A = 17 821 ± 14, B = 1425.526 ± 0.005, and C = 1353.909 ± 0.005MHz and the centrifugal distortion constants are D_J = 0.162 ± 0.010 and D_JK = ?10.28 ± 0.03kHz. Several series of vibrational satellite lines have been assigned to the torsional motions about the CH₂CH₂ and CH₂O bonds and to the CC≡N bending motion.     

Microwave spectrum of ethyl hypochlorite

The microwave spectrum of ethyl hypochlorite has been analyzed in detail in the region of 20–60 GHz. Observed transitions for C₂H₅O³⁵Cl in the ground state have been fit to a Hamiltonian model which includes p⁴ centrifugal distortion terms. The lowest vibrationally excited state of C₂H₅O³⁵Cl and the ground state and lowest vibrationally excited state of C₂H₅O³⁷Cl were analyzed with a rigid rotor model. This lowest vibrational mode lies at 125 ± 23 cm⁻¹ and is most likely the torsional motion about the CO bond. The dipole moment has been measured and found to have two nonzero components; μ_a = 1.623 ± 0.010 D, μ_b = 1.097 ± 0.005 D. No A-E torsional splittings were observed in either the ground state or the v = 1 state implying a lower limit for the barrier to internal rotation of ∼3.0 kcal/mole. Ethyl hypochlorite was synthesized in the waveguide by the reaction of chlorine nitrate with ethanol.     

Microwave spectrum of 2-chloropyridine

The microwave spectrum of 2-chloropyridine, C₅H₄NCl, has been studied in the frequency range from 26.5–40.0 GHz. The spectrum is characterized by strong parallel type transitions of a near-prolate asymmetric top. The assigned transitions have been used to evaluate the ground state rotational constants of the two chlorine isotopes. The rotational constants are (in MHz): A = 5872.52, B = 1637.83, C = 1280.48 for the ³⁵Cl isotopic species and A = 5872.16, B = 1591.76, C = 1252.17 for the ³⁷Cl isotopic species. The small inertial defect indicates the molecule is planar. In addition an excited vibrational state of C₅H₄N³⁵Cl has been observed and analyzed. The chlorine quadrupolar coupling constants were determined for the ground state and are: χ_aa = ?71.9 MHz for ³⁵Cl and χ_aa = ?54.9 MHz for ³⁷Cl. By assuming the pyridine ring structure the CCl bond length is found to be 1.72 Å.     

Microwave spectrum of phenyl isocyanate

The microwave spectra of the ground state and three excited states of the most abundant species of phenyl isocyanate have been recorded between 8 and 40 GHz. From ^aR-type transitions the ground-state rotational constants were calculated. The A value showed clearly a tilt of the NCO group from the C_2v axis. They yielded the r₀-type parameters. A centrifugal distortion treatment confirmed the validity of the rigid rotor approximation. The dipole moment components μ_a and μ_b were derived from the field strength dependence of six Stark lobes of five transitions. The values found were μ_a = (2.50 ± 0.02) D, μ_b < 0.2 D. From relative intensity measurements, the lowest vibrational excitation energies were determined. We assigned the lowest one to the NCO group torsion. All ^aR-type transitions of excited states were found unsplit by the internal rotation of the NCO group. The weakness of the μ_b dipole moment component and of the overall spectrum intensity did not allow us to find μ_b-type transitions and so, no splitting was observed on the ground-state spectrum. An evaluation of the V₂ high barrier is given.     

Microwave spectrum ofcis 3-fluorophenol

The microwave spectrum ofcis 3-fluorophenol involving rotational states up toJ=28 has been observed and analysed in the frequency range 23–25 GHz in the ground vibrational state at room temperature. Analysis yields three rotational and five quartic centrifugal distortion constants. A tentativer ₀ structure has been proposed satisfying the observed rotational constants. The small value of the inertia defect Δ=0·07 confirms the planarity of the conformer.     

Microwave spectrum of chloromethyl methyl ether

The microwave spectrum of chloromethyl methyl ether has been studied in the region 12.4–40 GHz. For ³⁵Cl species, a- and c-type transitions have been assigned for the ground state, the first excited state of the chloromethyl torsional mode, and the first excited state of the methyl torsional mode. Assignments were also made for the ground state of ³⁷Cl species. The assigned transitions are due to the gauche conformer. The nuclear quadrupole coupling constants were determined for the ground state of ³⁵Cl and ³⁷Cl species. The observed A-E splittings of the rotational transitions arising from the three vibrational states indicate a strong coupling between the two torsional vibrations. A model calculation based on the Hamiltonian previously used by Butcher and Wilson (J. Chem. Phys.40, 1671 (1964)), was carried out to account for the splittings and the vibrational frequencies of the two torsional modes. The barrier to internal rotation of the methyl group is estimated to be V₃ = 647 ± 17 cm^?1 (1.84 ± 0.05 kcal/mole).     

Microwave spectrum of the SF radical

The lowest rotational transition of the SF radical in the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ state has been observed and analyzed to determine the effective rotational constant B_eff and a magnetic hyperfine constant h to be 16 553.76₀ ± 0.052 MHz and 428.6₀ ± 0.71 MHz, respectively. The dipole moment was calculated from the Stark effects to be 0.79₄ ± 0.012 D.     

Microwave spectrum of gauche-isopropylphosphine

The microwave spectra of isopropylphosphine has been recorded in the region 12.4–40.0 GHz. Both a- and b-type transitions were observed and assigned. The rigid rotor rotational constants were determined to be A = 7633.34 ± 0.09, B = 4243.36 ± 0.02, and C = 3045.84 ± 0.02 MHz for (CH₃)₂CHPH₂ and A = 7226.47 ± 0.05, B = 4041.06 ± 0.02, and C = 2946.85 ± 0.02 MHz for (CH₃)₂CHPD₂. Dipole moment components of |μ_a| = 1.15 ± 0.01, |μ_b| = 0.43 ± 0.01, |μ_c| = 0.03 ± 0.02 and |μ_t| = 1.23 ± 0.01 were determined from the Stark effect. From the microwave spectra, the Stark effect and the experimental rotational constants, the assigned spectrum has been identified to result from the gauche form and this conformer is believed to be more stable than the other form which is present at room temperature.     

Microwave spectrum and conformation of thiomorpholine

The microwave spectrum of normal thiomorpholine (CH₂CH₂SCH₂CH₂NH) was investigated within the region 8–40 GHz, and that of N-deuterothiomorpholine (CH₂CH₂SCH₂CH₂ND) within the region 26.5–40 GHz. The observed spectra are due to the chair equatorial conformers. The rotational constants of both isotopic species were determined for the ground states and for two vibrationally excited states. The dipole moment components and quadrupole coupling constants of normal thiomorpholine and the iminohydrogen r_s coordinates were also determined.