The microwave spectrum of the DO2 radical

The a-type N = 1 ← 0,2 ← 1, and 3 ← 2 and the b-type 1₁₁ ← 2₀₂, 2₁₂ ← 3₀₃, 3₁₃ ← 4₀₄, 6₀₆ ← 5₁₅, and 7₀₇ ← 6₁₆ transitions, 14 in total, of the DO₂ free radical in the ground vibronic state were observed by microwave spectroscopy in the frequency region up to 200 GHz. The DO₂ radical was generated in a free-space absorption cell by a DC discharge in a mixture of CH₃OD and O₂. From the observed spectra the rotational constants, centrifugal distortion constants, spin-rotation coupling constants, and magnetic hyperfine coupling constants were determined with good precision. The hyperfine coupling constants of DO₂ were determined by the present work for the first time. A comparison of the in-plane components of the dipole-dipole interaction tensor of DO₂ with those of HO₂ made it possible to determine the off-diagonal component T_ab, and thus the principal values and the principal axes of the tensor.     

Microwave spectrum of the HO2 radical

Rotational transitions of the HO₂ free radical, a type 1₀₁ ← 0₀₀, 2₀₂ ← 1₀₁, 2₁₂ ← 1₁₁, and 2₁₁ ← 1₁₀, and b type 6₁₆ ← 7₀₇, 7₁₇ ← 8₀₈, 9₀₉ ← 8₁₈, and 10_0,10 ← 9₁₉, have been observed up to 137 GHz with microwave spectroscopy. The rotational constants, the centrifugal distortion constants in the symmetric-top approximation, the spin-rotation coupling constants, and the coupling constants of Fermi contact and dipole-dipole interactions are determined accurately. The absolute value of ?_ab + ?_ba, the off-diagonal component of the spin-rotation interaction tensor, is obtained from its second-order perturbation contributions to the spin doublings of the b-type rotational transitions. The small value of the Fermi contact parameter leads to the conclusion that the hydroperoxyl radical is a π-electron radical. The lowest two K-type doubling transitions, which are of particular interest to radioastronomy, are predicted on the basis of the molecular constants obtained.     

Microwave spectrum of PHD: hyperfine structure

The rotational spectrum of the monodeuterated PH₂ radical was studied using a source-modulated submillimeter-wave spectrometer. The PHD radical was generated in a free space absorption cell by a dc-glow discharge in a gas mixture of PH₃ and D₂. Six a-type and 20 b-type rotational transitions were observed in the frequency region of 170-670 GHz. Hyperfine structure due to the deuterium nucleus was resolved only in the rotational transitions of 1₁₁-0₀₀ and 1₁₀-1₀₁ and in the low F₂ components of N=2-1 transitions. A total of 219 spectral lines were measured of which 145 were analyzed by least-squares methods. These yielded 34 precise molecular constants including the hyperfine coupling constants of phosphorus, hydrogen, and deuterium. The principal axes and principal values of the magnetic dipole coupling tensors of hydrogen in PH₂ and deuterium in PD₂ were derived from the observed values of PHD, PH₂ and PD₂. The principal axis of the hydrogen magnetic dipole coupling tensor in PH₂ makes an angle of 2.29° with the PH bond and its T_σ and T_⊥ principal values are determined to be 12.93 and −18.39 MHz, respectively.     

The far infrared spectrum of 14N16O2

High resolution Fourier transform spectra in the 8–200 cm^-1 spectral region have been used to analyse the pure rotation spectrum of nitrogen dioxide. In this way, the spin rotation levels of the (000) state were accurately measured for K_a up to 14 and N up to 54. Using a hamiltonian which takes the spin-rotation and the hyperfine operators explicitly into account, it has been possible to derive a complete set of molecular parameters (rotational, spin-rotation and hyperfine constants) for the (000) state of ¹⁴N¹⁶O₂ from these experimental data and from the available microwave measurements. Numerous perturbations due to the hyperfine Fermi contact operator were analysed as well as a local resonance [42 0 42, J = 41·5] ? [41 2 40, J = 41·5] due to the electron spin-rotation interaction. Finally, a synthetic spectrum of the (000) ← (000) band of ¹⁴N¹⁶O₂ including all hyperfine transitions has been computed, covering the 0–235 cm^-1 spectral region.     

Doppler-limited dye laser excitation spectroscopy of the HSO radical

The cw dye laser excitation spectrum of the vibronic transition of the HSO radical was observed between 16 420 and 16 520 cm⁻¹ with Doppler-limited resolution, 0.03 cm⁻¹. The HSO radical was produced by reaction of discharged oxygen with H₂S or CH₃SH. The observed spectra were assigned to 751 transitions of the K′_a ← K″_a = 2 ← 3, 1 ← 2, 0 ← 1, 1 ← 0, 2 ← 1, and 3 ← 2 subbands, and were analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with good precision. The signs of the spin-rotation interaction constants were determined for both the upper and the lower state from the observed spectra. The band origin obtained is 16 483.0252 (2.5σ = 0.0013) cm⁻¹. The molecular constants which were determined reproduce the observed transitions with an average deviation of 0.0045 cm⁻¹.     

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 spectroscopy of chlorine dioxide: Centrifugal distortion,spin-rotation interaction,and hyperfine interaction constants of 35ClO2 and 37ClO2

Forty-six and fifty-five ground-state rotational transitions of ³⁵ClO₂ and ³⁷ClO₂, respectively, were newly identified in the frequency region of 8–75 GHz. Most of the absorption lines previously reported were remeasured. Centrifugal distortion constants up to sextic ones were derived for both isotopic species. In order to reproduce the observed fine structures satisfactorily, an analysis with the spin-rotation interaction Hamiltonian which included quartic as well as quadratic terms in (electronic spin or rotational) angular momenta was necessary. More precise hyperfine constants were also determined.     

Millimeter-Wave Spectroscopy of PO in Excited Vibrational States up to v=7

We have measured millimeter-wave transitions of PO, produced by the chemiluminescent reaction of oxygen with white phosphorus, P₄, in excited vibrational states up to v=7. We were hence able to obtain more precise rotational, spin-rotation, Λ-doubling, and hyperfine constants for this radical and better describe their vibrational dependence. The equilibrium PO bond length was determined as r_e=1.476 373 55(10) Å.     

Microwave Spectrum of the FCO Radical in the (2)A' Electronic Ground State

The 1(01)-0(00), 2(02)-1(01), and 3(03)-2(02) rotational transitions of the FCO radical are observed at 22.3, 44.5, and 66.8 GHz, respectively, using a Fourier transform millimeter-wave spectrometer with a pulsed discharge nozzle. The FCO radical is produced by discharging F(2)CO diluted in the Ar buffer gas. Twelve fine and hyperfine components for the three transitions are observed, and the effective rotational constant, the centrifugal distortion constant, the spin-rotation constant with its centrifugal correction term, and three hyperfine constants are determined. Furthermore, the vibrational satellites for the v(1)=1, v(2)=1, v(3)=1, and v(3)=2 states are also observed in the 22.3 GHz region. From the dipolar interaction constants, the principal axis of the dipolar interaction tensor is estimated and is discussed in relation to the distribution of the unpaired electron. Copyright 2001 Academic Press.     

Infrared diode laser spectroscopy of FCO: The ν1 and ν2 bands

The ν₁ (CO stretching) and ν₂ (CF stretching) bands of the FCO radical were observed with Doppler-limited resolution by an infrared diode laser spectrometer with Zeeman and source modulation. The FCO radical was generated by a 60-Hz discharge in one of the following three gas mixtures: O₂ + C₂F₄, CO + SF₆, and CO + C₂F₄, all diluted with He. The observed spectra were analyzed to determine the rotational constants, the centrifugal distortion constants, and the spin-rotation interaction constants. The band origins, 1861.6372(1) and 1026.1283(1) cm^?1 [with standard errors in parentheses], which were obtained, were found to agree well with matrix data, 1857 and 1023 cm^?1, respectively. The assignment of the observed spectra to the FCO radical was further supported by observing the ν₁ band of F¹³CO, which was obtained from ¹³CO and SF₆. The molecular structure and the force field of FCO are briefly discussed by using molecular constants obtained from the observed spectra.     

The microwave spectrum of sodium tetrahydroborate NaBH4 in excited vibrational states: Coriolis interaction between the Na-BH4 stretching and the BH4 rocking vibrations

Two sets of vibrational satellites have been observed in the rotational spectrum of sodium tetrahydroborate NaBH₄, and have been assigned to the non-degenerate, Na—BH₄ stretching and the degenerate BH₄ rocking (or internal rotation) states. The observation was extended from the J = 11 ← 10 up to J = 20 ← 19 transitions. The vibrational satellites showed anomalous K structure; higher-K lines of the non-degenerate state appeared at higher frequencies, in reverse to those of the ground state, whereas the spectra in the degenerate state exhibited a K pattern similar to but somewhat more widely spread than that of the ground state. These anomalies are ascribed to the Coriolis interaction between the two excited vibrational states. The spectra observed were analysed using a C_3v symmetric-top rotational Hamiltonian, which took into account the Coriolis interaction explicitly. The A rotational constants, the energy difference δE between the two interacting vibrational states, and the first- and second-order Coriolis interaction constants have been derived.     

Measurements of rotational transitions and hyperfine structure in PH2D

New rotational transition frequencies and measurements of hyperfine structure on two transitions are reported for PH₂D. All observed transitions are Q branch (ΔJ = 0) so only two independent rotational constants are obtained. These are A-C = 46 593.44 ± 0.67 MHz and κ(A-C) = 2B-A-C = ?34 545.9 ± 1.3 MHz. Nine transitions were fit to these parameters and the distortion parameter D_JK to obtain D_JK = 4.30 ± 0.04 MHz. Hyperfine structure due to spin-rotation interactions was observed on the 1₁₀ ← 1₁₁ transition at 6 024.645 MHz and on the 4₁₄ ← 4₀₄ transition at 20 815.334 MHz. Spin-rotation tensor components obtained are $\text{(M}{}_{\mathrm{aa}}\text{+ M}{}_{\mathrm{bb}}\text{)}\text{2}\text{=}\text{(M}{}_{\mathrm{aa}}\text{+ M}{}_{\mathrm{cc}}\text{)}\text{2}\text{= ?98 ± 3}\text{kHz}$.     

Microwave spectra of deuterated arsines: Distortion moment transitions of AsD3, microwave spectra of AsH2D and AsHD2, and the structure of arsine

Microwave spectra of three deuterated arsines have been measured and analysed. For AsD₃ distortion moment transitions have been observed for the first time, in the form of the K = ±1 ← ∓2 cluster; their frequencies have been combined with those of previously observed “normal” transitions to give rotational, centrifugal distortion, and ⁷⁵As hyperfine constants. For AsH₂D and AsHD₂, the measurements have been extended considerably and now include for the first time R-branch transitions; similar spectroscopic constants have been evaluated. The data have been combined with earlier results for AsH₃ and with vibrational data in a harmonic force field analysis. Both ground state average (r_z) and equilbbrium (r_e) structures have been estimated.     

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.     

Infrared diode laser and millimeter-wave spectroscopy of the NCl radical: Vibrational and isotopic dependences of molecular constants

The infrared diode laser and millimeter-wave spectra of the nitrogen chloride radical in the X³Σ⁻ state have been observed in a DC glow discharge plasma of a N₂ and Cl₂ mixture, yielding spectroscopic information on ¹⁴N³⁵Cl up to v = 4 and ¹⁴N³⁷Cl up to v = 3. The observed infrared and millimeter-wave spectra have been simultaneously included in a least-squares analysis to determine Dunham coefficients for the vibrational and rotational energies and similar terms for the fine structure interactions. The analysis has shown that isotopic relations based on the Born-Oppenheimer approximation do not hold for the vibrational frequency, the rotational constant, and the spin-spin and spin-rotation interaction constants. It has been found that the first derivative of the spin-spin interaction constant with respect to the internuclear distance is correlated with the change in the equilibrium internuclear distance caused by the b¹Σ⁺ ← X³Σ⁻ excitation.     

Doppler-limited dye laser excitation spectroscopy of the DSO radical

The $\text{A}\text{?}{}^2\text{A′(003) ←}\text{X}\text{?}{}^2\text{A″(000)}$ vibronic transition (16 370 to 16 425 cm^?1) of the DSO radical in studied by Doppler-limited dye laser excitation spectroscopy. DSO is produced in a flow system by reacting the products of a microwave discharge in O₂ with D₂S. About 637 observed lines are assigned to 987 transitions of the 19 subbands: K′_a ← K″_a = 6 ← 5, 5 ← 4, 4 ← 3, 3 ← 2, 2 ← 1, 1 ← 0, 0 ← 1, 1 ← 2, 2 ← 3, 3 ← 4, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 4 ← 4, 3 ← 1, 2 ← 0, 0 ← 2, and 1 ← 3. They are analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation constants for both the ground and the excited electronic states. The band origin obtained is 16 413.874 (2.5σ = 0.002) cm^?1. The rotational constants determined are combined with the previous result on HSO (M. Kakimoto et al., J. Mol. Spectrosc.80, 334–350 (1980)) to calculate the structural parameters for this radical in both the states: $\text{r(}\text{SO}\text{) = 1.494(5)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.389(5)}\text{A}\text{?}$, and ∠HSO = 106.6(5)° for the $\text{X}\text{?}{}^2\text{A″}$ state, and $\text{r(}\text{SO}\text{) = 1.661(10)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.342(8)}\text{A}\text{?}$, and ∠HSO = 95.7(21)° for the $\text{A}\text{?}{}^2\text{A′(003)}$ state, where values in parentheses denote 2.5σ.     

Infrared diode laser spectroscopy of the ν3 band of the fluoromethyl radical,CH2F

The ν₃ (CF stretching) band of the CH₂F radical was observed with Doppler-limited resolution, by using infrared diode laser spectroscopy with Zeeman and discharge current modulation. The CH₂F radical was generated directly in a multiple reflection absorption cell by the electrical discharge in CH₂FCOOCH₃. The observed spectrum was analyzed to yield the band origin of 1170.4165(6) cm⁻¹ with one standard error in parentheses, in addition to the rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the v₃ = 1 state.     

Microwave spectrum of nitrogen dioxide in excited vibrational states—Equilibrium structure

Microwave spectra were observed for ¹⁴NO₂ in the vibrationally excited ν₁, ν₂, ν₃, and 2ν₂ states, as well as for ¹⁵NO₂ in the ν₁ and ν₂ states. The rotational constants, spin-rotation coupling constants and hyperfine interaction constants were precisely determined. Second-order change of the spin-rotation coupling constants with respect to the bending vibrational quantum number v₂ was also determined. Combined use of the rotational constants obtained by the present microwave investigation and those reported in high-resolution infrared spectroscopic studies leads to the determination of all the vibration-rotation interaction constants α_s and γ_ss′ and the equilibrium structure of nitrogen dioxide, $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{N}\text{O) = 1.19389 ± 0.00004}\text{A}\text{?}$ and θ_e (ONO) = 133°51.4′ ± 0.2′, in the second-order approximation with respect to the vibrational quantum numbers.     

The microwave spectra of PH2D and PHD2, and the harmonic force field and structure of phosphine

Measurements of the pure rotational spectra of PH₂D and PHD₂ have been extended to include new Q-branch transitions and R-branch transitions. The rotational constants have been independently evaluated for the first time, along with some quartic and sextic centrifugal distortion constants. The spectrum of PD₃ has been reanalyzed to make the constants consistent with those reported for PH₃. The new results have been incorporated in a harmonic force field analysis. Both ground state average (r₂) and equilibrium (r_e) structures have been estimated.