Infrared emission spectrum and potential constants of HCl

The emission spectrum from a low-pressure hydrogen chloride flame has been recorded in the 3.1–5.3 μm region at high resolution using a 4.5-m grating spectrometer coupled to a PDP-15 computer. The data obtained for the v → v - 1 band sequence, with v = 1 to 6 for H³⁵Cl and v = 1 to 5 for H³⁷Cl, were combined with other accurate data and analyzed to obtain the vibrational and rotational constants and Dunham coefficients for the H³⁵Cl and H³⁷Cl molecules. Using this information, eighth-order nonlinear least-squares estimates of the Dunham, Simons-Parr-Finlan, Ogilvie, and Sandeman potential constants were computed. While the values of all four sets of constants display a lack of convergence, the constants of Sandeman's expansion exhibit better statistical behavior than the other three. This suggests that a Sandeman-like inversion of the Simons-Parr-Finlan and Ogilvie potential constants would be worthwhile.     

Rotational spectra, nuclear quadrupole hyperfine tensors, and conformational structures of the mustard gas simulent 2-chloroethyl ethyl sulfide

Rotational spectra have been recorded for both the ³⁵Cl and ³⁷Cl isotopic forms of two structural conformations of 2-chloroethyl ethyl sulfide (CEES). The rotational constants of the ³⁵Cl and ³⁷Cl isotopomers were used to identify the conformational isomers. A total of 236 hyperfine transitions have been assigned for 47 rotational transitions of the ³⁵Cl isotope of a GGT conformer, and 146 hyperfine have been assigned for 37 rotational transitions of the ³⁷Cl isotopomer. For the second conformer, a total of 128 (110) hyperfine and 30 (28) rotational transitions have also been assigned to the ³⁵Cl (³⁷Cl) isotopes of a TGT conformation. The extensive hyperfine splitting data, measured to high resolution with a compact Fourier transform microwave spectrometer, were used to determine both the diagonal and off-diagonal elements of the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors in the inertial tensor principal axis system. The experimental rotational constant data, as well as the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors, were compared to the results from 27 optimized ab initio (HF/6-311++G^∗∗ and MP2/6-311++G^∗∗) model structures.     

The pure rotational spectrum of ZnCl (XΣ): Variations in zinc halide bonding

The radical ZnCl (X²Σ⁺) has been studied using millimeter-wave direct-absorption techniques. Pure rotational spectra of ⁶⁷Zn³⁵Cl, ⁶⁶Zn³⁷Cl, ⁶⁸Zn³⁵Cl, ⁶⁴Zn³⁵Cl, ⁶⁴Zn³⁷Cl, and ⁶⁶Zn³⁵Cl were measured in the vibrational ground state and data were also recorded for the latter three in the v = 1 and v = 2 states. Every rotational transition was found to be split into a doublet due to spin-rotation interactions. For ⁶⁷Zn³⁵Cl, each doublet exhibited additional splittings arising from hyperfine coupling of the ⁶⁷Zn (I = 5/2) nucleus. Rotational, fine structure, and hyperfine constants have been determined from these data, and equilibrium parameters calculated. The equilibrium bond length of ⁶⁴Zn³⁵Cl is found to be 2.13003305(24) Å, in good agreement with recent theoretical predictions. Interpretation of hyperfine constants indicates that the 12σ orbital is ∼70% Zn(4s) in character, suggesting that the zinc chloride bond is relatively ionic.     

Pure rotational spectrum, ab initio anharmonic force field, and equilibrium structure of silyl chloride

The ground state rotational spectra of H₃Si³⁵Cl, H₃Si³⁷Cl, and D₃Si³⁵Cl have been measured from the microwave to the submillimeterwave ranges and accurate rotational parameters have been determined. For H₃Si³⁷Cl, they are in good agreement with the values obtained from the ground state combination differences. The quadratic, cubic, and semi-diagonal quartic force field has been calculated at the MP2 level of theory employing a basis set of polarized valence quadruple-zeta quality. This force field has been used to predict the spectroscopic constants. The calculated values are found to be in good agreement with the available experimental data. The equilibrium structure has been derived from the experimental ground state rotational constants and either the ab initio or the experimental rovibrational interaction parameters. These experimental and semi-experimental structures are in excellent agreement with the ab initio equilibrium geometry.     

Microwave spectra of eight isotopic modifications of 1-chloro-1-fluoroethylene

The rotational spectra of eight isotopomers of 1-chloro-1-fluoroethylene in the 6-22 GHz region have been collected and analyzed. Each rotational transition is split into hyperfine components by the chlorine (either ³⁵Cl or ³⁷Cl) nuclear quadrupole coupling interaction and additionally, one or more smaller interactions such as the spin-rotation interaction due to the fluorine atom, hydrogen-hydrogen spin-spin coupling interactions, and in appropriately substituted species, the deuterium nuclear quadrupole hyperfine interaction. The rotational constants derived from these isotopomers allow the determination of average and Kraitchman substitution structures for 1-chloro-1-fluoroethylene, whereas the availability of the diagonal chlorine nuclear quadrupole coupling constants for all the isotopomers provides complete quadrupole coupling tensors for both ³⁵Cl and ³⁷Cl. In the course of this work, the rotational spectrum of an excited vibrational state of the normal isotopomer was observed, which ab initio calculations suggest should be assigned to ν₉=1, an in-plane bending motion at the CFCl end of the molecule.     

Spectral intensities in the fundamental bands of HF and HCl

The transition intensities of the fundamental bands of natural isotopic HF and HCl vapors have been measured with Doppler-limited resolution using a tunable difference-frequency laser spectrometer. Precise values for the band intensities, vibrational moments and Herman-Wallis F factors have been obtained for H¹⁹F, H³⁵Cl and H³⁷Cl.     

The microwave spectrum of HGeCl

The J = 1₀₁-0₀₀ and 2₀₂-1₀₁ transitions of nine isotopomers of chlorogermylene, H⁷⁴Ge³⁵Cl, H⁷⁴Ge³⁷Cl, H⁷²Ge³⁵Cl, H⁷²Ge³⁷Cl, H⁷⁰Ge³⁵Cl, H⁷⁰Ge³⁷Cl, H⁷⁶Ge³⁵Cl, H⁷⁶Ge³⁷Cl, and H⁷³Ge³⁵Cl are measured at 8-9 and 16-18 GHz. The effective rotational constants, the nuclear quadrupole coupling constants of ³⁵Cl, ³⁷Cl, and ⁷³Ge, and the nuclear spin-rotation coupling constants of ³⁵Cl and ³⁷Cl are determined.     

Microwave spectra of the Cl and Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin-rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C³⁵Cl³⁷Cl and C³⁷Cl₂ of dichloromethylene in the ground vibronic state were recorded in the range 10-33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl₂ was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin-rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C³⁵Cl₂ [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50-55.] a refined r₀ structure was determined. The spin-rotation interaction constants of all three isotopomers were used to derive ³⁵Cl and ³⁷Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.     

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.     

Rotational spectrum of C chloromethanes

Rotational spectra of 13 carbon chloromethane isotopologues ¹³CH₃³⁵Cl and ¹³CH₃³⁷Cl with resolved hyperfine structures were measured in the spectral region from 50 GHz to 275 GHz. An estimated uncertainty of individual well developed lines was better than 5 kHz. Ground state molecular parameters B, D_J, D_JK, H_J, H_JK, H_KJ, eQq, and C_N were derived. Determination mainly of the hyperfine constants is significantly better than in previous studies.     

Nuclear quadrupole coupling in chloroform and calibration of ab initio calculations

The complex hyperfine structures in the J = 1 ← 0, and J = 2 ← 1 ground state rotational transitions of ³⁵Cl₃CH and ³⁵Cl₂³⁷ClCH were resolved and measured at conditions of supersonic expansion. Accurate spectroscopic constants for the two isotopomers have been derived from global fits of the hyperfine structure together with hyperfine-free high-J millimetre wave data. The complete inertial and principal quadrupole tensors of the chlorine nuclei have been determined, and the symmetric top treatment for ³⁵Cl₃CH and the asymmetric top treatment for ³⁵Cl₂³⁷ClCH yield identical results for the principal tensor components of the ³⁵Cl nucleus. The availability of precise experimental splitting constants for many molecules allows benchmarking of ab initio field gradient calculations, and it is found that for the chlorine nucleus optimum predictive performance for molecules of moderate size is obtained at the B3LYP/aug-cc-pVDZ level by using a scaling factor of 1.0619(23).     

Assignment and analysis of the rotational spectrum of 3-chlorobenzonitrile

The rotational spectrum of 3-chlorobenzonitrile has been assigned and measured over the frequency region 9-290 GHz, both in the static sample and in supersonic expansion. Extensive measurements are reported for the ground states of the ³⁵Cl and the ³⁷Cl isotopomers. Precise spectroscopic constants have been determined from global fits to all available data, including resolved hyperfine splitting structure due to the presence of the chlorine and the nitrogen quadrupolar nuclei. Principal nuclear quadrupole tensors are derived for both ³⁵Cl and ¹⁴N nuclei in the parent isotopomer, and the results are compared with those for related molecules. The values of all spectroscopic constants are confronted with predictions from ab initio calculations in order to assess the utility of the array of simple techniques employed to increase quantitative accuracy of such predictions.     

Pure rotational spectra of 32SF535Cl, 32SF537Cl,and 34SF535Cl up to 300 GHz

Pure rotational spectra of the three molecules ³²SF₅³⁵Cl, ³²SF₅³⁷Cl, and ³⁴SF₅³⁵Cl in their ground vibrational states have been observed up to 300 GHz (8 < J < 80). Molecular parameters have been computed with good accuracy for the three isotopic species. The “K-type” splitting characteristic of molecules belonging to the C_4v symmetry group has been clearly seen and measured.     

Pressure broadening and shift of transitions of the first overtone of HCl

High-resolution spectroscopic measurements were made using distributed feedback diode lasers. We measured line strength and pressure-induced broadening and shift for two lines, R(3) and P(4), of the first overtone (2?0) ro-vibrational band, for the two isotopomers H³⁵Cl and H³⁷Cl, according to their natural abundances; measurements were also made in the presence of foreign gases. Comparison was made with available data when possible. Received: 29 February 2000 / Published online: 8 November 2000     

Two-dimensional (2 + n) REMPI of HCl: Observation and characterisation of a new Rydberg state

Two-dimensional REMPI data, obtained by recording ion mass spectra for HCl as a function of two-photon wavenumber, revealed a previously unobserved (2 + n) REMPI spectra for H³⁵Cl and H³⁷Cl with band origin for H³⁵Cl at 82 521.2 cm⁻¹. Analysis of the data, involving simulation calculations, relative ion-yield determinations laser-power-dependence measurements and comparison with earlier experimental and theoretical work allowed the upper state to be assigned as the g³Σ⁺(1), v′ = 0 Rydberg state with  = 10.26 cm⁻¹ for H³⁵Cl.     

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 and molecular force field of tetratomic C2v molecules: NO2Cl

The rotational constants and quartic centrifugal distortion constants for NO₂³⁵Cl and NO₂³⁷Cl have been determined from an analysis of rotational transitions in the microwave and millimeter wave regions between 8.2–40 and 90–120 GHz, respectively.The values of the in-plane force constants in the general harmonic potential field have been obtained by combination of infrared and microwave data. Vibrational frequencies of ¹⁴NO₂Cl and ¹⁵NO₂Cl, inertia defects of NO₂³⁵Cl in the excited vibrational states v₃ = 1 and v₅ = 1, and first-order centrifugal distortion constants of NO₂³⁷Cl are the experimental data used in the least-squares fitting determination of force constants.     

Absorption profiles of HCl for the J = 1-0 rotational transition: Foreign-gas effects measured for N2, O2, and Ar

Line profiles of the J = 1-0 transition of the hydrogen chloride, H³⁵Cl and H³⁷Cl isotopomers, were measured with a BWO-based submillimeter-wave spectrometer at AIST in real form: three hyperfine transitions for each isotopomer, i.e., total six lines at 625 and 626 GHz. The effect of foreign gases on the broadening and shift was determined for N₂, O₂, and Ar. The modified Voigt function was applied as the line shape function for preliminary analysis, where the collisional-narrowing effect was clearly observed. In the final analysis, we applied the Galatry function and determined the integral intensity, line center position, Lorentzian width, and contraction parameter for each absorption line. The magnitudes of the foreign-gas pressure-broadening coefficients decrease in order of N₂, O₂, and Ar. The line-shift coefficients were clearly observed, the magnitudes of which decrease in order of Ar, O₂, and N₂. The pressure dependence of contraction parameter was determined, although with poor precision.     

The Lamb-dip spectrum of methylcyanide: Precise rotational transition frequencies and improved ground-state rotational parameters

Methylcyanide, CH₃CN, is an important interstellar species, and therefore the accurate knowledge of precise rest frequencies for rotational transitions as well as ground-state rotational and hyperfine constants is needed. In this work the hyperfine structure of the millimeter- and submillimeter-wave spectra of CH₃CN has been further investigated. In addition, accurate THz measurements have been carried out for the first time. Consequently, the present investigation allowed us to provide the most accurate ground state rotational and hyperfine parameters known at the moment for CH₃C¹⁴N. To resolve the hyperfine structure of the rotational transitions observed, the Lamb-dip technique has been exploited. Both frequency-modulated and video-type detections have been employed.     

Centrifugal distortion constants and force field of HClCO

Measurement of the a- and b-type rotational transitions of formyl chloride, HClCO, was extended up to J = 50 and k_a = 5 ← 4 in the frequency range of 8 to 200 GHz. Accurate rotational parameters including the sextic centrifugal distortion constants were determined from the observed spectrum for the ³⁵Cl and ³⁷Cl species. The τ defect in the planarity relations of the quartic centrifugal distortion constants was found to be negligibly small. From the quartic centrifugal distortion constants and the previously reported fundamental vibrational frequencies, force constants of formyl chloride were calculated by assuming the Urey-Bradley force field.