Observation and analysis of fundamental bending mode of T2O

The absorption spectrum of the ν₂ band of T₂O vapor has been observed at 0.04 cm^?1 resolution. A total of 549 transitions has been assigned; 474 of these have been used to evaluate the rotational constants A, B, and C as well as the fourth-order and sixth-order distortion constants and one eighth-order constant for the upper vibrational state.     

The ν2 fundamental vibration-rotation band of T2O

The ν₂ fundamental vibration-rotation band of T₂O vapor has been measured at grating resolution, and the rotational structure has been analyzed. The band center and the values of the rotational constants A, B, and C for the ground state and excited state have been determined. These values are consistent with the data for J through 6, and with extrapolation from H₂O and D₂O.     

The microwave spectrum of CHD2Cl

The ground vibrational state microwave spectrum of CHD₂Cl has been studied in the region 26.5–40.0 GHz. From the observation of weak c-type transitions the A₀ rotational constants of CHD₂³⁵Cl and CHD₂³⁷Cl have been determined to be 95 426.08 ± 0.06 and 95 425.23 ± 0.11 MHz, respectively. The observed a-type and c-type transitions have been used to obtain A, B, C, all five quartic and one sextic distortion constants present in the reduced Hamiltonian of Watson for the ³⁵Cl and ³⁷Cl isotopic modifications of CHD₂Cl.     

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.     

Diode laser spectrum and analysis of the 882-cm−1 band of s-tetrazine

A high-resolution diode laser spectrum of the 882-cm^?1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10^?5 cm^?1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν₁₂ to ν₁₄.     

Determination of the spin-spin centrifugal distortion parameters for deuterated selenoformaldehyde in its first excited triplet state

Recently-formulated centrifugal distortion corrections to the spin-spin Hamiltonian have been used to analyse the first excited triplet state (ã³A₂) of deuterated selenoformaldehyde. By including six spin-spin centrifugal distortion parameters, it is possible to account for the energy levels of this state using a single set of three rotational constants, A, B, and C, where previously nine spin-dependent parameters were required.     

Pure rotational spectra of allene-1, 1-d2 and allene-d1 observed by microwave Fourier transform spectroscopy

Pure rotational transitions of allene-1, 1-d₂ and allene-d₁ in their vibronic ground state have been observed with a pulsed microwave Fourier transform spectrometer for the 8- to 18-GHz frequency range. Thirteen new transitions of allene-1, 1-d₂ with J up to 32 have been assigned. The measured transition frequencies have been combined with earlier measurements of Hirota and Matsumura [J. Chem. Phys. 59, 3038–3042 (1973)] in a least-squares fit of the rotational constants B and C and the centrifugal distortion constants Δ_J, Δ_JK, δ_J, and δ_K. Fifteen transition of allene-d₁ with J up to 34 have been assigned. The rotational constants A, B, and C, and the quartic centrifugal distortion constants Δ_J, Δ_JK, Δ_K, δ_J, and δ_K have been determined from the measured frequencies in a least-squares fit.     

Analysis of the fundamental asymmetric stretching mode of T2O

The ν₃ mode of T₂O, observed at 0.04 cm⁻¹, has been analyzed. By an iterative process of fitting and assignment 210 lines were assigned; 167 of these were used in the final fitting. The standard deviation of the fit is 0.023 cm⁻¹. The rotational constants, A, B, and C, as well as the quartic distortion constants, have been evaluated for the excited state.     

The rotational a-type sepctra of 15N-labeled diazirine,H2CN2

The rotational a-type spectra of isotopically enriched diazirine isotopomers, H₂¹²C¹⁴N¹⁵N and H₂¹²C¹⁵N₂, have been recorded in the region between 8 and 300 GHZ; the latter isotopomer has been observed for the first time. Using Watson's A-reduced Hamiltonian, the rotational constants and the quartic and some sextic centrifugal distortion constants have been determined for the ground vibrational states.     

Microwave spectrum and hydrogen bonding in 2-dimethylaminoethanol

The microwave spectrum of the normal species of 2-dimethylaminoethanol gives rotational constants (MHz) A = 5814.0(2), B = 2214.54(2), and C = 2037.96(2) and a dipole moment of 2.56 D, with a, b, and c components (D) of 2.27(2), 0.3(1), and 1.16(5), respectively, consistent with a gauche OCCN configuration, and an OH?N type hydrogen bond, facilitated by a central CN configuration distorted approximately 23° from “staggered.” The hydroxy d₁ species rotational constants (MHz) A = 5688.95(38), B = 2190.17(4), and C = 2028.00(4) are consistent with either the hydroxyl group structure $\text{r}\text{OH = 1.235}\text{A}\text{?}$ and COH = 100.5° or a structurally normal hydroxyl group with an approximate 0.01 ÅrO?N shrinkage upon deuteration.     

The microwave spectrum,dipole moment,and molecular conformation of 2-cycloheptene-1-one

The microwave spectrum of 2-cycloheptene-1-one, an unsaturated cyclic ketone, has been studied in the regions 26.5–40 and 7.0–12.4 GHz. An analysis of the ground-state “a”-type transitions yielded the rotational constants (in MHz): A = 2997.27, B = 2049.24, C = 1399.76. The “a”-type transitions of an excited vibrational state were also assigned, giving A = 3000.51, B = 2046.65, C = 1398.88. The centrifugal distortion constants, D_J and D_JK, were needed to fit the data adequately. A study of the Stark effect yielded the dipole moment components (in debye) μ_a = 3.63 ± 0.023 and μ_c = 0.882 ± 0.040. The μ_b component could not be determined from the Stark effect data. These data are used to discuss the molecular conformation of cycloheptene-1-one.     

Microwave spectral study of the axial and equatorial conformers of cyanocyclopentane

The microwave spectrum of cyanocyclopentane has been observed and analyzed in the 26.5 to 40.0-GHz frequency region. Rotational transitions were assigned for both an axial and an equatorial conformer. These data and those for the molecule deuterated in the 1-position (1-d-cyanocyclopentane) show that both conformers adopt the C_s envelope structure. For the normal isotopic species the rotational constants have the following values, in megahertz: axial, A = 4297.196, B = 2210.245, C = 2057.205; equatorial, A = 6324.905, B = 1790.937, C = 1497.792. Relative intensity measurements indicate that the ground-state energy difference of the two conformers is 0 ± 200 cal/mole. The low-frequency (pseudorotational) potential surface has been discussed and compared with that of chlorocyclopentane.     

Microwave spectrum and selenol internal rotation of 2-propaneselenol

Microwave spectra of 2-propaneselenol and its deuterated species were measured and assigned for the gauche and trans isomers. The double minimum splittings of the gauche isomers were directly observed from b-type transitions, which were assigned with the aid of a double resonance technique. Rotational constants and torsional splitting of the gauche isomer of the parent species were determined to be A = 7802.50 ± 0.75, B = 2847.68 ± 0.04, C = 2242.03 ± 0.03, ΔA = ?2.52 ± 0.74, ΔB = 0.02 ± 0.05, ΔC = ?0.34 ± 0.03, and Δν = 368.91 ± 0.94 MHz, where ΔA, and ΔB, and ΔC are the differences of the rotational constants between the (+) and (?) states. From the torsional splittings and the energy differences of the two isomers of the parent and SeD species, Fourier coefficients of the selenol internal rotation potential function were determined to be V₂ = ?88 ± 15, V₃ = 1543 ± 29 cal/mole on the assumption of V₁ = 0. Dipole moments and their components were also obtained for the two isomers.     

The microwave spectrum,structure and nuclear quadrupole coupling constants for stibabenzene

The microwave spectrum of 121-SbC₅H₅, 123-SbC₅H₅, β-dideutero 121-SbC₅H₃D₂ and 123-SbC₅H₃D₂ has been assigned in the region 26.5–40.0 GHz. The respective rotational constants and uncertainties are: A = 4512.69 ± 0.42, B = 1738.00 ± 0.01, C = 1254.51 ± 0.01; A = 4512.84 ± 0.30, B = 1729.80 ± 0.01, C = 1250.22 ± 0.01; A = 4176.18 ± 0.33, B = 1660.94 ± 0.01, C = 1188.15 ± 0.01; A = 4176.60 ± 0.61, B = 1652.94 ± 0.03, C = 1184.03 ± 0.03 (in MHz units). The structure is found to be planar, C_2v in symmetry. The $\text{d(}\text{Sb-C}\text{) = 2.050 ± 0.005}\text{A}\text{?}$ and ∠CSbC = 92.9° ± 1.0°. The nuclear quadrupole coupling constants for the 121 and 123 antimony isotopes are χ_aa = 456.4 ± 4.1 MHz, η = 0.396 ± 0.008, and χ_aa = 583.00 ± 5.3 MHz, η = 0.399 ± 0.008, respectively. Several alternate techniques using the coupling constants as data support a σ-donating property for antimony.     

The microwave spectrum and dipole moment of heptafulvene

The microwave spectrum of heptafulvene (C₈H₈) has been investigated in the frequency range from 26 to 40 GHz. The following rotational constants have been obtained from a least-squares fit of the measured transition frequencies: A = 3665.972(66)MHz, B = 2004.3165(59)MHz, and C = 1297.5029(90)MHz. From the corresponding moments of inertia it was concluded that heptafulvene has a planar equilibrium structure. The quantitative measurement of the Stark splittings of three transitions have yielded a dipole moment of 0.477(5) D along the a principal axis. A series of satellite transitions accompanied each rotational transition. The satellites have been assigned to the lowest out-of-plane vibration ν₄₂ (B₂) for which a frequency of 70(11) cm^?1 has been determined from relative intensity measurements.     

The harmonic force field and rz structure of HNCO

The presently available microwave, millimeter wave, and far-infrared data of five isotopic species of isocyanic acid, namely, HNCO, H¹⁵NCO, HN¹³CO, HNC¹⁸O, and DNCO, have been used to obtain improved values of the ground-state rotational constants, the five quartic distortion constants, and some higher-order distortion constants in the I^rS reduced Hamiltonian of Watson. The appropriate planarity relation among the quartic centrifugal distortion constants has been imposed in the fitting procedure. The general harmonic force field of isocyanic acid has been determined using all existing data, and assuming a trans bent equilibrium geometry of the molecule with an NCO angle of 170°. Finally an r_z structure has been obtained using the A_z, B_z, and C_z rotational constants of five isotopic species. The bending of the NCO chain is found to be 8° in the trans configuration.     

Rotational Analysis of the ÃA1-X?A1 Band System of Yttrium Dicarbide, YC2

The 000-000 and 3¹₀ bands of the 775-nm electronic transition of YC₂(òA₁←X?²A₁) have been studied at high resolution, using the laser-induced fluorescence from a supersonic jet expansion. Three types of experiment have been carried out. First, the complete rotational and hyperfine structures of the two bands were recorded. To measure the small asymmetry splittings in the K=2 levels of the X?²A₁ state, portions of the b-type 3¹₀ band were then recorded in the presence of a weak static electric field. Finally, a number of pure rotational transitions between the K=0 levels of the ground state were recorded by pump/probe microwave optical double resonance. A few small rotational perturbations occur in the upper electronic state but, omitting the perturbed lines, the combined data sets could be modeled using an effective Hamiltonian operator appropriate for the rotation, electron spin, and hyperfine structure of a rigid asymmetric top molecule. The molecule is confirmed as being “T-shaped,” where the Y atom is bonded to the side of a C₂ group; the rotational constants determined are for the òA₁, 3¹ level, A=1.76128, B=0.189949, C=0.170056 cm⁻¹, and for the X?²A₁, v=0 level, A=1.742731, B=0.201947, C=0.181285 cm⁻¹. Allowing for electron orbital corrections to the rotational constants, the geometrical structures are found to be òA₁ state, r (Y-C)=2.2795 Å, r (C-C)=1.2630 Å, ∠C-Y-C=32.17°; X?²A₁ state, r (Y-C)=2.1946 Å, r (C-C)=1.2697 Å, ∠C-Y-C=33.63°. A molecular orbital diagram is given for the states of YC₂ and the interpretation of the electron spin and hyperfine parameters is discussed.     

Microwave spectrum of CHD2CN and CHD2NC,and the harmonic force field and rz structure of methyl cyanide and isocyanide

The microwave spectra of CHD₂CN and CHD₂NC have been measured from 18 to 40 GHz; about 20 type A and 30 type C transitions have been observed for each molecule. These have been fitted to a Hamiltonian using 3 rotational constants, and 5 quartic and 4 sextic distortion constants, in the I^rS reduction of Watson [in “Vibrational spectra and structure” Vol. 6 (1977)]; the standard error of the fit is 26 kHz. For methyl cyanide the 5 quartic distortion constants have been used to further refine the recent harmonic force field of Duncan et al. [J. Mol. Spectrosc.69, 123 (1978)], but the changes are small. Finally, for both molecules, the harmonic force field has been used to determine zero point average moments of inertia I_z from the ground state rotational constants for many isotopic species, and these have been used to determine an r_z structure. The results are compared with r_s structure calculations.     

Microwave spectral studies of rotational isomerism in substituted ethanethiols: 2-Aminoethanethiol and 2-chloroethanethiol

Microwave spectra were observed and analyzed for 2-aminoethanethiol and 2-chloroethanethiol. The amino compound exists in two gauche rotameric conformations, one exhibiting an intramolecular SH?N hydrogen bond. The hydrogen-bonded conformer lies higher in energy by 274 ± 90 cal mole^?1 and has the following rotational constants (in MHz): A = 12 040.1 ± 11.3, B = 3352.24 ± 0.03, and C = 2881.99 ± 0.03. For the non-hydrogen-bonded conformer the rotational constants (in MHz) are A = 11 929.9 ± 10.2, B = 3395.01 ± 0.03, and C = 2877.82 ± 0.03. Dipole moment measurements for the H-bond conformer led to μ_a = 2.68 D, μ_b = 0.88 D, and μ_c = 0.37 D, while for the non-H-bond form the values are μ_a = 1.51 D, μ_b = 0.0 D, and μ_c = 0.62 D. In the case of chloroethanethiol, the only assigned spectral lines were the unresolved J → J + 1 a-type bands of a trans conformation. For this molecule the combination rotational constant B + C has the value 2955.17 ± 0.02 MHz for the ³⁵Cl species and 2879.73 ± 0.02 MHz for the ³⁷Cl species.     

The force field and rz structure of Ketene

Recently determined Coriolis coupling constants for H₂ and D₂ Ketene, centrifugal distortion constants for H₂, HD, and D₂ Ketene have enabled 16 of the 19 parameters in the general force field of Ketene to be determined with significance, the ambiguity between the choice of two sets of A₁ and B₁ species force constants being removed. The r₀ structure has been redetermined using the latest values of the rotational constants of H₂, HD, and D₂ Ketene and an r_z structure has been determined for the first time.