Laser Stark and laser microwave double-resonance spectroscopy of deuterated fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of deuterated fluoroacetylene was identified with the aid of the double-resonance technique for the ν₃, ν₃ + ν₅ ? ν₅, ν₃ + ν₄ ? ν₄, ν₃ + 2ν₅ ? 2ν₅, and ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅ vibrational bands. Laser microwave double-resonance signals were observed in the presence of the Stark field. From the analysis of the double-resonance signals precise values of the dipole moment were obtained for 10 vibrational states, in Debye, with the uncertainties in parentheses: ground, 0.73292(22); ν₅, 0.75656(17); ν₄, 0.68412(24); 2ν₅(Σ⁺), 0.78063(21); ν₄ + ν₅(Σ⁺ or Σ^?), 0.70698(19); ν₃, 0.75772(30); ν₃ + ν₅, 0.78270(18); ν₃ + ν₄, 0.70822(17); ν₃ + 2ν₅(Σ⁺), 0.80808(25); ν₃ + ν₄ + ν₅(Σ⁺ or Σ^?), 0.73329(17). The band origins were determined (in cm^?1); ν₃, 1045.9242(8); ν₃ + ν₅ ? ν₅, 1049.6441(8); ν₃ + ν₄ ? ν₄, 1047.8700(8); ν₃ + 2ν₅ ? 2ν₅(Σ⁺-Σ⁺), 1053.0374(8); ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅(Σ⁺?Σ⁺ or Σ^??Σ^?), 1051.5040(8).     

Laser Stark spectroscopy of thioformaldehyde in the 10-μm region: The ν3, ν4, and the ν6 fundamentals

The ν₃, ν₄, and ν₆ bands of thioformaldehyde, H₂CS, have been studied using the technique of laser Stark spectroscopy. The H₂CS was produced by the pyrolysis of dimethyl disulfide, and the spectrum was observed using a multipass absorption cell. The band origins are ν₃, 1059.2037 cm^?1; ν₄, 990.1866 cm^?1; and ν₆, 991.0149 cm^?1. The band previously assigned as 2ν₆ has been reassigned as 2ν₂, leading to a value of the ν₂ band origin of ca. 1439 cm^?1. Rotational constants and dipole moments of the vibrational states have been determined.     

Laser Stark spectroscopy of FCN

Using a CO₂ laser, Stark shifted resonances have been measured for the CF stretching fundamental (ν₃) of FCN near 9.3 μm, and for two nearby “hot” bands. The band centers measured are 1076.492007 ± 0.000013 cm^?1 for 00⁰1-00⁰0, 1085.741046 ± 0.000050 cm^?1 for 01¹1-01¹0, and 1091.16222 ± 0.00015 cm^?1 for 02⁰1-02⁰0. The ground state dipole moment of FCN is found to be 2.1203 ± 0.0010 D and dipole moments are also given for the other states observed. Values are given for the rotational constant and l-doubling constant for the 01¹1 state.     

Tunable laser diode study of the ν3 band of SiF4 near 9.7 μm

Doppler-limited tunable-diode laser spectra of the stretching fundamental ν₃ of ²⁸SiF₄ near 1031 cm^?1 were analyzed and the spectroscopic constants determined. The ν₃ vibrational dipole moment derivative was determined for several rovibrational lines.     

Carbon suboxide: The infrared spectrum from 1800 to 2600 cm−1

The infrared spectrum of carbon suboxide has been recorded from 1800 to 2600 cm^?1 at a resolution of 0.003 cm^?1. About 7% of the ca. 40 000 lines observed have been assigned and analyzed, belonging to 36 different bands. Most of these are associated with the fundamental ν₃, at 2289.80 cm^?1, and the combination band ν₂ + ν₄, at 2386.61 cm^?1, each of which give rise to a system of sum bands, difference bands, and hot bands involving the low-wave-number fundamental ν₇ at 18 cm^?1. A few other tentative assignments are made. The bands have been analyzed for vibrational and rotational constants.     

Stark spectroscopy with the CO laser: The ν2 fundamental bands of trans- and cis-nitrous acid,HNO2, in the 6-μm region

The ν₂ fundamental bands of trans- and cis-HNO₂ have been studied by the technique of intracavity CO laser Stark spectroscopy. Excited-state rotational constants were determined, and the ν₂-band origins were found to be 1699.760 cm^?1 for the trans isomer and 1640.517 cm^?1 for the cis isomer. The total dipole moments for the ground and excited (v₂ = 1) vibrational states were found to be μ″ = 1.930 D and μ″ = 1.852 D for trans-HNO₂, and μ″ = 1.428 D and μ″ = 1.441 D for cis-HNO₂.     

The ν4 and ν2 Raman bands of CHD3

The CHD₃ Raman spectrum from 1925 to 2455 cm^?1 has been photographed with a resolution of about 0.2 cm^?1, showing the overlapping ν₂ and ν₄ bands. Ground state combination differences yield C₀ = 2.6297 ± 0.0003 cm^?1. The ν₄ state is weakly perturbed, but reasonably accurate values could be obtained for ν₄ = 2250.88 ± 0.10 cm^?1, (Cζ)₄ = 0.656 ± 0.010 cm^?1, C₄ - C₀ and B₄ - B₀. Some of these constants differ significantly from values previously estimated by infrared workers. For the ν₂ state the constants determined are in good agreement with recent infrared results.     

High-resolution measurements of the 1 ← 0 infrared absorption band of hydrogen iodide

The ν₁ fundamental band of FNO has been studied by the technique of CO laser Stark spectroscopy. The band origin was determined to be 1844.099 cm^?1, and values for the rotational and centrifugal distortion constants of the (100) excited vibrational state were found. The ground state dipole moment components were determined to be μ_a = 1.690 and μ_b = 0.370 D, for a total dipole moment of 1.730 D, and a relatively large reduction (5%) was found in μ for the (100) state relative to the ground state.     

High resolution diode laser measurements on the ν2 bands of 14NH3 and 15NH31

More than 500 lines in the ν₂ bands of ¹⁴NH₃ and ¹⁵NH₃ have been measured in the region 740–1200 cm^?1 with a diode laser spectrometer, with an accuracy better than 0.0005 cm^?1 for most of the lines. Wavenumbers (in cm^?1) were determined using a 3-in. Ge etalon for calibration and OCS, N₂O, NH₃, and CO₂ lines as references. The diode laser data were combined with pure inversion and inversion rotation frequencies and sets of rotational constants were obtained by the method of merged least squares. Perturbations between the Δk = ±3 levels have been taken into account in these calculations.     

Laser microwave double resonance spectroscopy of OCS with a 9.4-μm CO2 laser: Precise measurement of dipole moment in the 0310 vibrational state

A CO₂ laser microwave double resonance experiment in the presence of an intense Stark field was applied to the 01¹0 and 03¹0 vibrational states of the OCS molecule. The precise dipole moment of the 03¹0 state, 0.68173 ± 0.00020 D, was determined. The 03¹0←01¹0 band origin was obtained as 1052.94429 ± 0.00020 cm^?1. This technique is very useful for accurate calibration of the space between Stark electrodes.     

High resolution infrared spectrum of the ν4 band of DCCF

The bending vibration-rotation band ν₄ of DCCF was studied. The measurements were carried out with a Fourier spectrometer at a resolution of about 0.03 cm^?1. The constants B₀=0.29141(1)cm^?1, α₄=?5.02(2)×10^?4cm^?1, q₄=4.52(3)×10^?4cm^?1, and D₀=9.2(4)×10^?8cm^?1 were derived. The rotational analysis of the “hot” bands 2ν₄(Δ) ← ν₄(II) and 2ν₄(Σ⁺) ← ν₄(II) was performed. In addition, the “hot” bands ν₄ + ν₅ ← ν₅ were assigned. A set of vibrational constants involved was derived.     

Doppler-limited spectra of the CH stretching fundamentals of formaldehyde

The Doppler-limited spectrum of H₂CO in the 2700 to 3000 cm^?1 region has been recorded using a tunable difference-frequency laser system. This region encompasses the ν₁ and ν₅ fundamental CH stretching bands of formaldehyde as well as a number of strongly interacting combination bands. The tunable laser spectrometer affords complete spectral coverage with a calibration precision better than 10^?3 cm^?1 for the transition frequencies and with absolute absorption intensity measurements better than 2%. The band centers for the ν₁ and ν₅ vibrations are measured to be 2782.4572 ± 0.0010 cm^?1 and 2843.3254 ± 0.0015 cm^?1 respectively, independent of the upper-state rotational constants.     

Diode laser spectrum of diacetylene near 5 μm

The ν₅ rotation-vibration fundamental band and the ν₅ + ν₉ band of diacetylene in the region 2000–2037 cm^?1 have been measured to an accuracy of better than ±0.004 cm^?1 using a tunable-diode laser spectrometer. The l-type doubling in the (ν₅ + ν₉ ? ν₉ band has been resolved. Line positions, assignments, band origins, and rotational constants B′_v, B″_v, D′_v, and D″_v are reported.     

Observation of the v = 1 ← 0 band of SH (X2Π) with a difference frequency laser

The fundamental vibration-rotation band of SH (X²Π) has been studied in absorption at Doppler-limited resolution with an estimated accuracy of 0.002 cm^?1. The band origin (ν₀ = 2598.7675 ± 0.0003 cm^?1) and the molecular constants for the excited vibrational state (v = 1), as well as improved molecular constants for the ground vibrational state, have been determined in a least-squares fit.     

Stark spectroscopy with the CO2 laser: The ν5 band of 12CD3F

The ν₅ band of ¹²CD₃F was studied using coincidences with the 9.4-μm band of the ¹²C¹⁶O₂ laser and the 9.25-μm band of the ¹²C¹⁸O₂ laser. The resonances were analyzed together with the infrared spectra and recent microwave results to give the following vibration-rotation parameters and dipole moment in the ν₅ state: ν₀ = 1072.35093 (11) cm^?1; B = 0.681137 (4) cm^?1; A₅-A₀ = ?0.01437 (3) cm^?1; Aζ_z = ?0.81453 (3) cm^?1; μ_ν5 = 1.8751 (25) D. The parameters should be useful in assigning some near millimeter laser lines in CD₃F.     

The bending vibration bands ν4 and ν5 of HCCI

The bending vibration bands ν₄ and ν₅ of HCCI were studied. From the observed rotational structure the rotational constant B₀ and the centrifugal distortion constant D₀ were obtained. The results were B₀ = 0.105968(7) cm^?1 and D₀ = 1.96(7) × 10^?8 cm^?1 from ν₄ and B₀ = 0.105948(8) cm^?1 and D₀ = 1.96(11) × 10^?8 cm^?1 from ν₅. The structure of the hot bands 2ν₅(Δ) ← ν₅(Π) and 3ν₅(φ) ← 2ν₅(Δ) was also resolved and hence the values α₅ = ?3.033(8) × 10^?4 cm^?1 and q₅ = 9.3(3) × 10^?5 cm^?1 could be derived. The other most intense hot bands following ν₅ could be explained in terms of the Fermi diads $\text{ν}{}_3\text{2ν}{}_5{}^0$ and $\text{ν}{}_3\text{+}\text{ν}{}_5{}^{\mathrm{\pm 1}}\text{3ν}{}_5{}^{\mathrm{\pm 1}}$. Of the numerous hot bands accompanying ν₄, only those between different excited states of ν₄ could be assigned. Then estimates for α₄ and q₄ were also obtained. In addition, several vibrational constants were derived.     

Analysis of the ν2 + ν3 band of 12CH4 and 13CH4

The ν₂ + ν₃ bands of ¹²CH₄ and ¹³CH₄ occurring in the region 4400–4650 cm^?1 have been studied from spectra recorded with a high-resolution Fourier transform spectrometer (resolution better than 0.01 cm^?1). Champion's Hamiltonian expansion, Canad. J. Phys.55, 1802 (1977), is applied to the problem of the two interacting F₁ and F₂ vibrational sublevels of this type of a band. As the P branch of ν₂ + ν₃ is strongly overlapped by neighboring bands, a combination-difference method, adapted to tetrahedral XY₄ molecules has been developed to help assignments of lines. A fit of 700 transitions has been performed using 13 new effective constants in the case of ¹²CH₄. In the case of ¹³CH₄, 532 transitions have been fit to 18 constants. The known parameters, relative to the vibrational ground state and the ν₃ state for both methanes, and the ν₂ state for ¹²CH₄ were fixed throughout. Most of the perturbed levels, up to J′ = 12, are well reproduced and the general agreement between experimental and calculated transitions is satisfactory with standard deviations of 0.047 cm^?1 (¹²CH₄) and 0.041 cm^?1 (¹³CH₄). The results (order of magnitude of obtained (ν₂ + ν₃) parameters and comparison of observed and computed intensities) indicate that the ν₂ + ν₃ band is perturbed by many other bands.     

Diode laser spectrum of HCCl near 5 μm: The ν2 fundamental and accompanying hot bands

The CC stretching band ν₂ of iodoacetylene has been studied by tunable laser spectroscopy in the range of 2037–2071 cm^?1. The hot bands associated with the low-lying bending vibrations ν₄ and ν₅ were observed. For the Π-Π hot bands, the splitting caused l-type doubling was resolved for high J transitions. For the fundamental band the hyperfine splittings due to the ¹²⁷I nuclear quadrupole moment were clearly observed for R(0) and P(1) transitions. Combination of these diode laser spectra with the microwave data allows precise determination of the constants in the ground and excited vibrational states.     

The infrared spectrum of C3O2: The interaction between ν7 and the ν2 and ν4 vibrations

The 3ν¹₇, 3ν³₇, and 4ν⁰₇ hot bands of the ν₄ fundamental of C₃O₂ in the 1580 cm^?1 region were analyzed from tunable diode laser spectra and the ground state to ν₄ + 2ν⁰₇ band at 1644 cm^?1 from Fourier transform spectra (FTS). The molecular constants for all of the v₄ 1 ← 0 bands as well as the intensity of the ν₀ + 2ν⁰₇ sum band relative to the ν₄ fundamental were in agreement with the predictions of the model of Weber and Ford. FTS spectra at 0.05 cm^?1 resolution were obtained of the sum and difference bands of ν₂ with ν₇ in the 750–900 cm^?1 region. Sharp Q branches occur for each ν₇ state in the sum bands, but only a number of R-branch bandheads and no recognizable Q branches in the difference bands. Assignments of the sum band Q branches through v₇ = 6 were made and molecular constants were determined for the ν₂ + ν¹₇ ← 0 transition at 819.7 cm^?1. The ν₇ potential function in the v₂ = 1 state was found to have a 1.2 cm^?1 barrier with a minimum at α = 4.9°, where 2α is the angular deviation from linearity. The Q-branch positions predicted from the calculated energy levels fit those observed within several cm^?1.     

High-resolution laser Stark and Fourier transform spectroscopy of the ν2 fundamental band of HFCO

The ν₂ (CO stretch) fundamental band of formyl fluoride (HFCO) was studied in the region 1800 to 1910 cm^?1 using the two techniques of intracavity CO laser Stark spectroscopy at sub-Doppler resolution and Fourier transform spectroscopy at Doppler-limited resolution. Accurate values of the molecular parameters of the ground and excited (v₂ = 1) vibrational states were obtained from a combined fit of the ν₂ band data and available microwave data. The results include precise determinations of the electric dipole moment components (μ_a and μ_b) of HFCO in the ground and excited states.