Observed Line Frequencies Research Articles

Pure rotational spectrum of HCI

The 101–000 and 202–101 rotational transitions of a monohalomethylene, HCI, are observed in a discharge plasma of diiodomethane by Fourier-transform microwave (FTMW) and FTMW-microwave double-resonance spectroscopy. The effective rotational constant (B+C)/2, the centrifugal distortion constant ΔJ, and the quadrupole coupling constant of the iodine nucleus are determined from the observed line frequencies. The nuclear spin-rotation coupling constant Cbb is required to be included into the set of fitting parameters for a satisfactory analysis of the observed line frequencies.

The hyperfine structure of NO(A2Σ+)

Hyperfine quantum beat spectroscopy has been combined with an effective Hamiltonian approach to determine the hyperfine structure of NO(A,v). NO(A,v=0,N=1–7,9J=1.5–8.5,F=0.5–8.5) was produced by pulsed dye laser excitation on the 0–0 band of the NO A2Σ+←X2Π transition at wavelengths around 226nm. The observed line frequencies, along with those reported in previous measurements of NO(A,v=0,3) have been fitted using a non-linear least-squares program with numerical diagonalization of the Hamiltonian matrix. This enabled us to determine the best obtainable sets of hyperfine parameters for the molecule. The vibrational dependence of the hyperfine parameters is discussed in the light of previous experimental and theoretical work on related systems.

Submillimeter-wave spectrum of carbonyl sulfide: rare isotopic species

Rotational spectra of four rare isotopic species of OCS were observed in the 110–690GHz region with a source-modulated submillimeter-wave spectrometer. Spectral lines of 18O13CS, O13C36S, 18OC36S, and 18O13C34S were measured in their natural abundances, 21.4, 1.51, 0.29, and 0.95ppm, respectively. The rotational constants and centrifugal distortion constants were precisely determined from observed line frequencies by least squares methods. In order to facilitate sensitivity examination in the submillimeter-wave region, transition frequencies and peak absorption coefficients were calculated and tabulated for the spectral lines of the four species up to the 1000GHz region.

AsyrotWin: A 32-bit Windows version of Asyrot, A program for the analysis of high resolution singlet-singlet band spectra of asymmetric tops

A new version of the Asyrot program has been written to extend the computational limits to J=999 and K a=450 and to include the octic, M K , and N K centrifugal distortion constants. The number of transitions calculated and fitted is limited only by available computer memory. Two new phases have been added to the program so that the parameters of a single state can be refined by forming combination differences and then fitting them, along with any available microwave lines, to the appropriate Hamiltonian. A new Windows interface has been integrated with the Fortran code to greatly facilitate the editing of the input data. A limited Windows based band contour plotting and comparison feature has been added. Two utility features are also available. The first allows for the easy transfer of observed line frequencies to the corresponding transition quantum labels listed in the input file. The second allows for the summation of several calculated spectra, of different bands or isotopomers, into an overall contour which can be compared to an observed spectrum.

Infrared spectra of the C2H2–HCl complexes: An experimental and ab initio study

By means of a pulsed slit jet and an infrared tunable diode laser spectrometer, the vibration–rotation absorption spectra of the complexes C2H2–H35Cl and C2H2–H37Cl have been observed for the first time in the 3.6 μm region of the ν1 band correlated with the HCl stretch. All the lines of the spectrum have been assigned for J=0 to 18 and Ka=0, 1, 2, 3. To determine the band origin and the rotational and centrifugal constants, the observed line frequencies have been fitted to those determined by the Watson Hamiltonian in the A reduction. A force constant model has been used to derive the binding energy De of the complex and the intermolecular stretching harmonic frequency from the experimental spectroscopic constants. The available experimental results concerning these complexes and other isotopic forms D35Cl and D37Cl were compared with ab initio calculations performed at the coupled-cluster single double triple [CCSD(T)] level of theory. The comparison turned out to be very good for all the properties considered (geometries, frequencies, energies).

Microwave spectroscopic detection of transition metal hydroxides: CuOH and AgOH

Pure rotational spectra of transition metal hydroxides have been reported. Millimeter wave spectra of CuOH and AgOH were recorded in a direct current discharge absorption cell in the range of 200–390 GHz. The spectra of both molecules correspond to that of a near prolate asymmetric top and only a-type R branch transitions were observed. The rotational and centrifugal distortion constants of CuOH and AgOH were precisely determined. Centrifugal distortion terms up to N2Nz10 were required to fit the observed line frequencies of CuOH63. A preliminary analysis showed that AgOH is also strongly bent like CuOH with a bond angle smaller by about 2°.

The microwave spectrum and equilibrium conformation of phthalan

The microwave spectrum of phthalan has been observed in the frequency range of 18–70 GHz. The spectra of the ground and ten excited vibrational states have been assigned and rotational and quartic centrifugal distortion constants have been obtained from semirigid rotor fits to the observed line frequencies. The microwave spectrum is not consistent with either the C2v equilibrium conformation deduced from the far infrared spectrum or the C2 equilibrium conformation obtained from the single vibronic level fluorescence spectra. The microwave data indicates that the bending of the five membered ring is a very anharmonic vibration with a double minimum potential function with a low barrier and that phthalan therefore has a Cs equilibrium conformation. The previous spectroscopic data can be reinterpreted in a manner consistent with this and gives a barrier height of 38 cm-1. The twisting of the five membered ring is a reasonably harmonic vibration and its fundamental wave-number is ∼ 180 cm-1. The microwave dat...

Laboratory microwave spectrum of the cyclic C3D radical

The rotational spectral lines of the cyclic C3D radical in the 2B2 electronic ground state are detected in the laboratory. The radical is produced by discharging a gaseous mixture of C2D2, Co, and He, and the spectrum is observed in the 148-360 GHz region. The molecular constants including hyperfine coupling constants due to the D nucleus are determined by the least-squares analysis from 52 observed line frequencies. The frequencies of several low-N transitions needed for future radioastronomical observations are calculated from the molecular constants.

N_2O vibration–rotation parameters derived from measurements in the 900–1090-and 1580–2380-cm^−1 regions

The N2O infrared spectrum in the 900–1090- and 1580–2380-cm−1 regions was studied at a 0.005-cm−1 resolution with a Fourier-transform spectrometer. Measurements were made of line frequencies of the species 14N216O, 14N15N16O, 15N14N16O, 14N218O, 14N217O, 15N216O, 14N15N18O, and 15N14N18O for several ground-state bands and hot bands. A few of these bands are reported for the first time to the author’s knowledge. The observed line frequencies were analyzed to obtain values of band centers and upper-state effective rotational constants. Results from the least-squares fits for the 0400–0000, 0420(e)–0000, and 0510–0110 bands of the 14N216O molecule indicate that the high-J levels of the upper states are perturbed. Resonance interactions were observed in transitions in the 1001–1000 band of 14N216O and 15N14N16O and the 1111(f)–1110(f), 0600–0200, 0600–1000, and 0620(e)–1000 bands of 14N216O.

The barrier to internal rotation of the methyl group in methyl thiolformate from microwave spectroscopy

Some low- J μ a R-branch lines of the E torsional substate of the ground vibrational state of methyl thiolformate were assigned. Calculations using the Internal Axis Method (IAM) and the Principal Axis Method (PAM) reproduce the observed line frequencies within a few MHz. The barrier to internal rotation of the methyl group is determined to be 1.78 ± 0.03 kJ mole −1.

The microwave spectrum of the OH X2Π radical in the ground and vibrationally-excited (ν ≤ 6) levels

The microwave absorption spectrum of the OH X2Π radical has been observed in all vibrational levels up to ν = 6. Experimental details are described of the tunable cavity and parallel plate Stark-modulated spectrometers employed for transitions below and above 23 GHz, respectively. The observed line frequencies, together with those reported by other workers, have been fitted using a non-linear least-squares routine with numerical diagonalization of the Hamiltonian matrix. Pseudo high-order corrections for centrifugal distortion of the Λ-doubling are required for the ν = 0 data, which now extend to J = 19/2 in the 2Π1/2 component. The various adjustable parameters of the Hamiltonian are compared with those of other similar models. The Λ-doubling and magnetic hyperfine constants for the different vibrational levels are reported, and several line frequencies of potential astrophysical significance are predicted.

The A2Σ +- X2Π i electronic band system of the OD free radical : Spectroscopic data for the 0-0 sequence, and rotational term values for A2Σ + and X2Π i

The A 2Σ +- X 2Π i emission system of the OD radical has been recorded at high resolution from a discharge through flowing D 2O at 0.1 torr pressure. The 0-0, 1-1, and 2-2 bands of the Δ v = 0 sequence have been analyzed in detail for the first time. A table of the vacuum wavenumbers and wavelengths in air of the rotational lines of these bands is presented, together with some additional measurements for the 0–1 band. The data are used to obtain a self-consistent set of term values for v′ and v″ = 0, 1, which reproduces the observed line frequencies with an average deviation of less than 0.02 cm −1. Earlier, lower resolution data for bands with v′ and v″ = 2, 3 are also combined with the present measurements to give approximate term values for these higher levels.

L-Type Doubling Transitions in HCN and DCN

Direct transitions between levels split by $l$-type doubling have been observed for $J=9,10,\mathrm{and} 11$ in HCN and for $J=10,11,\mathrm{and} 12$ in DCN. The $l$-type doubling coefficient calculated from the observed line frequencies shows a slight decrease with increasing $J$ for both molecules. While the observed values of the $l$-type doubling coefficient $q$ are in good agreement with those calculated theoretically, the slight variation of $q$ with $J$ was not expected. This variation of $q$ with increasing $J$ involves a negative term in $q$ proportional to $J(J+1)$ and may therefore be related to the effects involved in centrifugal stretching of the rotating molecule.