Fourier transform infrared spectrum of the ν3 band of HCO

The ν₃ fundamental band of the formyl radical, HCO, in the 5.3-μm region has been observed at high resolution (0.0025 cm⁻¹, unapodized) using a Fourier transform spectrometer. The HCO radicals were formed by the reaction of F atoms with H₂CO in a fast-flow multiple-traversal absorption cell. A total of 298 lines were measured with an accuracy of about 0.0004 cm⁻¹ and assigned to transitions with values of the rotational quantum numbers N and K_a up to 20 and 5, respectively. These data greatly improve the knowledge of the HCO ν₃ line positions and (v₁v₂v₃) = (001) vibrational state molecular parameters as compared to earlier laser magnetic resonance studies of this band, especially for higher values of N. The ν₁ fundamental band of HCO was also observed and an analysis of these data agrees well with the recent study of Dane et al. [J. Chem. Phys. 88, 2121–2128 (1988)].     

The ν1 and ν3 stretching fundamental bands of PD3

The infrared (IR) spectrum of PD₃ has been recorded in the 1580–1800 cm⁻¹ range at a resolution of 0.0027 cm⁻¹. About 2400 rovibrational transitions with J^′=K^′22 have been measured and assigned to the ν₁ (A₁) and ν₃ (E) stretching fundamentals. These include 506 “perturbation-allowed” transitions with selection rules Δ(k−l)=±3. Splittings of the K^′′=3 lines have been observed. Effects of strong perturbations are evident in the spectrum. Therefore the rovibrational Hamiltonian adopted for the analysis explicitly takes into account the Coriolis and k-type interactions between the v₁=1 and v₃=1 states, and includes also several essential resonances within these states. The rotational structure in the v₁=1 and v₃=1 vibrational states up to J^′=K^′=18 was reproduced by fitting simultaneously all experimental data. Thirty-four parameters reproduced 1950 transitions retained in the final cycle with a standard deviation of the fit equal to 4.9 × 10⁻⁴ cm⁻¹ (about the precision of the experimental measurements).     

Transition dipole moment measurements for the ν2 band of NH3 with molecular beam laser Stark spectroscopy

Rabi oscillations were observed in the ASR(110), ΔM = 0 and ASQ(222), ΔM = 0 transitions of the ν₂ band of ¹⁴NH₃ in a molecular beam crossed by a CO₂ laser beam. The frequency (in terms of the laser field amplitude) of the oscillations was used to determine the transition dipole moment of the ν₂ band, yielding μ_s←a = 0.261 ± 0.006 D. The hyperfine structure due to the electric quadrupole interaction of the nitrogen nucleus was clearly resolved.     

The Electric Dipole Moment of the CO2–CO van der Waals Complex

Radiofrequency transitions withinK= 2 asymmetry doublets have been observed for the CO₂–CO van der Waals complex. A Stark effect measurement on theJ= 2,K= 2 transition provides an electric dipole moment of μ = 0.2493(1) D. Combining this result with the permanent moment of CO, μ_CO= 0.1098 D, gives a change of moment on complex formation of Δμ = 0.140 D. The sign of Δμ is such that the CO end of the complex is more positive than CO₂. The origin of Δμ should not be attributed to any single mechanism, and several different contributions to Δμ are discussed.     

High-resolution FTIR spectroscopy of HNSO—Analysis of the highly perturbed ν4, ν6 and 2ν5 bands

We report a rovibrational analysis of the ν₄ and ν₆ fundamentals and the 2ν₅ overtone of HNSO from high-resolution Fourier transform infrared spectra. The ν₆ band (out-of-plane bend) centred at 757.5 cm⁻¹ is c-type. The ν₄ band (HNS bend) centred at 905.9 cm⁻¹ is predominantly a-type with a very weak b-type component (). Numerous global perturbations and localized avoided crossings affecting the v₄ = 1 rotational levels were successfully treated by inclusion of Fermi and c-axis Coriolis resonance terms between v₄ = 1 and v₅ = 2, and a b-axis Coriolis resonance term between v₄ = 1 and v₆ = 1. The latter term gives rise to an avoided crossing with an extraordinary ΔK_a = 5 selection rule. The Fermi resonance between v₄ = 1 and v₅ = 2 gives rise to strong mixing of their rotational wavefunctions in the vicinity of K_a = 18. The resultant borrowing of intensity made it possible for 2ν₅ transitions in the range K_a = 16–19 to be assigned and included in a global rovibrational treatment of all three band systems.     

Line Positions and Intensities of the ν1+ ν2+ 3ν3, ν2+ 4ν3, and 3ν1+ 2ν2Bands of Ozone

Using a Fourier transform spectrometer, we have recorded the spectra of ozone in the region of 4600 cm⁻¹, with a resolution of 0.008 cm⁻¹. The strongest absorption in this region is due to the ν₁+ ν₂+ 3ν₃band which is in Coriolis interaction with the ν₂+ 4ν₃band. We have been able to assign more than 1700 transitions for these two bands. To correctly reproduce the calculation of energy levels, it has been necessary to introduce the (320) state which strongly perturbs the (113) and (014) states through Coriolis- and Fermi-type resonances. Seventy transitions of the 3ν₁+ 2ν₂band have also been observed. The final fit on 926 energy levels withJ_max= 50 andK_max= 16 gives RMS = 3.1 × 10⁻³cm⁻¹and provides a satisfactory agreement of calculated and observed upper levels for most of the transitions. The following values for band centers are derived: ν₀(ν₁+ ν₂+ 3ν₃) = 4658.950 cm⁻¹, ν₀(3ν₁+ 2ν₂) = 4643.821 cm⁻¹, and ν₀(ν₂+ 4ν₃) = 4632.888 cm⁻¹. Line intensities have been measured and fitted, leading to the determination of transition moment parameters for the two bands ν₁+ ν₂+ 3ν₃and ν₂+ 4ν₃. Using these parameters we have obtained the following estimations for the integrated band intensities,S_V(ν₁+ ν₂+ 3ν₃) = 8.84 × 10⁻²²,S_V(ν₂+ 4ν₃) = 1.70 × 10⁻²², andS_V(3ν₁+ 2ν₂) = 0.49 × 10⁻²²cm⁻¹/molecule cm⁻²at 296 K, which correspond to a cutoff of 10⁻²⁶cm⁻¹/molecule cm⁻².     

Diborane : High resolution infrared rovibration studies of B2H6 and B2D6

Ground state rotation and quartic distortion constants were obtained for ¹¹B₂D₆ from the analysis of high resolution (0.05 cm⁻¹) Fourier transform infrared spectra. The bands studied comprised the ν₁₇, ν₁₈ type A, and ν₁₄, ν₉ + ν₁₅ type C bands of ¹¹B₂H₆ and the ν₁₆, ν₁₇, ν₁₈ type A, ν₈ type B, and ν₁₄ type C bands of ¹¹B₂D₆. In the case of ¹¹B₂H₆, the authors' ground state data were combined with those of Lafferty et al. obtained from a previous study (J. Mol. Spectrosc. 33, 345–367 (1970)) at comparable resolution of the ν₁₆ type A and ν₈ type B fundamentals. Information on the ground state rotational energy manifold of ¹¹B₂H₆ was accumulated up to J = 23, K_a = 18, and of ¹¹B₂D₆ up to J = 32, K_a = 22. This permitted rather precise determination of the distortion constants Δ_J⁰, Δ_JK⁰, Δ_K⁰, although δ_J⁰ and δ_K⁰ proved to be too small (< 10⁻⁷ cm⁻¹) and were constrained to values calculated from the force field. Sets of upper state parameters were determined for all vibrational levels studied. Although these appear to be essentially unperturbed globally, several localized perturbations were observed and identified.     

The high resolution infrared spectrum and laser Stark spectroscopy of thev8 band of propyne

The perpendicularv ₈ band lying in the 1000–1100 cm^–1 region has been studied from infrared and laser Stark, spectra. We were interested in the part of spectrum corresponding to the spectral range of the 9 m CO₂ laser lines. Assignments of rovibrational lines with J'<40 and K'<6 have been made. About 100 Stark resonances have been assigned to 12 rovibrational transitions. Effective molecular constants and dipole moment have been determined with high accuracy. A list of close resonances with CO₂ laser lines is given and may be used for optical pumping experiments.     

The high-resolution infrared spectra of the ν2 and ν3 bands of HOCl

The infrared spectra of the a-type transitions of the ν₂ and ν₃ bands of HO³⁵Cl and HO³⁷Cl have been obtained under high resolution. Line assignments of both bands have been made, and the spectroscopic constants have been obtained for both bands using a Watson Hamiltonian. Lines of the K_a = 5 subband of the ν₂ band of the HO³⁵Cl molecule were found to be slightly shifted by an interaction with the K_a = 4 level of the 2ν₃ vibrational state. The b-type transitions permitted for both bands were too weak to observe. Relative intensities of selected lines of both bands have been measured, and empirical Herman-Wallis factors have been determined.     

The 2ν8 Band of CH3CN

The overtone band 2ν⁰₈ of CH₃CN around 720 cm⁻¹ has been measured on a Bruker Fourier transform spectrometer at a resolution of 0.003 cm⁻¹. Only the parallel band was observed, but due to the l(2, 2) resonance, ΔK = −2 lines leading to the v₈ = 2, l₈ = −2 levels with K = 1-3 could be seen. More information for the l₈ = ±2 component of the vibrational state v₈ = 2 was evaluated from the hot band 2ν^±2₈ - ν^±1₈. Altogether more than 1000 lines were assigned. In the fit pure rotational lines from literature were also combined. Among the results the anomalous A₀ - A′ values 4.6722(13) × 10⁻³ cm⁻¹ for the 2ν⁰₈ band and 7.0324(32) × 10⁻³ cm⁻¹ for the 2ν^±2₈ band are striking.     

Narrow saturation resonances in the spectrum of OsO4 induced by CO2 laser radiation

Narrow saturation resonances in the v₃ band of the rotational-vibrational spectrum of the OsO₄ molecule were observed in the radiation field of a number of lines of the CO₂ laser. The parameters and relative positions of narrow resonances offer the possibility for further improvement of the long-term frequency stability of the CO₂ laser. The OsO₄ molecule is considered a suitable medium for finding the effect suggested by Letokhov; it consists in the γ-radiation narrow resonances on nuclear transitions of Os under the effect of excitation of OsO₄ molecular oscillations by the CO₂ laser radiation.     

High-resolution infrared study of the 2ν3 (A1, E) and ν1 + ν3 (E) bands of NF3

The 2ν₃ overtone (A₁, E) and the ν₁ + ν₃ (E) combination bands of the oblate symmetric top ¹⁴NF₃ were studied by FTIR spectroscopy with a resolution of 2.5 × 10⁻³ cm⁻¹. Nearly 500 lines up to K_max/J_max = 30/43 were observed for the weak A₁ component reaching the v₃ = 2⁰ substate (1803.1302 cm⁻¹), the majority of which corresponded to reinforced K = 3p-type transitions. For the strong E component reaching the v₃ = 2^±2 substate (1810.4239 cm⁻¹), about 3550 transitions were assigned up to K_max/J_max = 65/69, favoring a clear observation of the ℓ(4, −2) and ℓ(4, 4) splittings within the kℓ = −2 and +4 sublevels, respectively. The two v₃ = 2 substates are linked by the ℓ(2, 2)- and ℓ(2, −1)-type interactions, providing severe crossings, respectively, at K′ = 6 and near K′ = 24 on the v₃ = 2⁺² side. A model working in the D-reduction and including all these ℓ-type interactions could reproduce together 3695 nonzero weighted experimental data (NZW) through 33 free parameters with a standard deviation of σ = 0.357 × 10⁻³  cm⁻¹. As for the ν₁ + ν₃ (E) combination band, about 3690 lines were assigned up to K_max/J_max = 45/55. Its v₁ = v₃ = 1 upper state (1931.577 5 cm⁻¹) was treated using the same model recently applied to the v₃ = 1 (E, 907.5413 cm⁻¹) state. It yielded 21 free parameters through 3282 NZW experimental data, adjusted with σ = 0.344 × 10⁻³  cm⁻¹ in the D-reduction. For the two excited states, the small and unobserved ℓ(0, 6) interaction was tested as useless. To confirm the adequacy of the vibrationally isolated models used, some other reductions of the Hamiltonian were tried. For the v₃ = 2 state, the D-, L-, and LD-reductions led to similar σ’s, while the Q one was not successful. For the v₁ = v₃ = 1 state, the D- and Q-reductions gave comparable σ’s, while the QD-reduction was not as good. The corresponding unitary equivalence relations are generally more nicely fulfilled for the v₃ = 2 state than for the v₁ = v₃ = 1 state. The three derivable anharmonicity constants in cm⁻¹ are x₃₃ = −4.1528, g₃₃ = +1.8235 and x₁₃ = −7.9652.     

The A2 (n, 3px) Rydberg state of formaldehyde

Pairs of bands were observed in the absorption spectrum of H₂CO, HDCO, and D₂CO in the 1470-1430 Å region which were characterized by well-defined rotational band contours. A band contour synthesis of the observed band envelopes demonstrated that the bands are described by type C selection rules. From the observed intervals and their shifts on deuterium isotope substitution these bands were assigned to quantum additions of ν₅ and ν₆. The symmetry of the upper state was deduced to be ¹A₂ from the vibrational assignment of the bands and their polarizations, while the results from MO theory lead to the orbital assignment n → 3p_x. The electronic transition then is .     

High-resolution infrared spectrum and analysis of the ν2 band of CF3Cl

The rotational structure of the ν₂ band of CF₃Cl, with natural isotopic abundance, has been investigated using a tunable diode laser spectrometer. The spectra have been obtained for a low-temperature (200 K) sample, to reduce the interfering contributions of hot-band transitions. Due to the very small value of the (ΔA − ΔB) constant for both isotopic species, the K structure of most P(J) and R(J) multiplets is generally not resolvable. Only for CF₃³⁵Cl, the K structure could be resolved for P(J) multiplets with J≥55. Molecular constants for the ν₂ fundamental of both isotopic species have been obtained using least-squares fitting routines in combination with band contour simulations for unresolved K structure.     

Analysis of the ν9/ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm⁻¹) on a Fourier transform instrument in the region 730 to 1170 cm⁻¹ containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from −6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = −10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.     

The far-infrared spectrum and spectroscopic parameters of PH3 in the ground state

The far-infrared spectrum of phosphine, PH₃, was recorded in the region between 30 and 200 cm⁻¹ at a resolution of 0.002 cm⁻¹. ΔJ = +1, ΔK = 0 rotational transitions in the ground state were measured and assigned up to J″ = 22 and K = 19. These transitions were analyzed together with the presently available microwave and submillimeter-wave data on the basis of different formulations of the rotational Hamiltonian, which included Δk = ±3 and/or Δk = ±6 interaction terms. An upper limit for the constant of the inversion splitting was obtained by fitting the same transitions to an appropriate inversion-rotational Hamiltonian. Rotational transitions in the v₂ = 1 and v₄ = 1 vibrational states were also observed.     

High-Resolution Infrared Spectra of the ν2, ν3, ν4, and 2ν3 Bands of SO3

New measurements are reported for the infrared spectrum of sulfur trioxide, ³²S¹⁶O₃, with resolutions ranging from 0.0015 cm⁻¹ to 0.0025 cm⁻¹. Rovibrational constants have been measured for the fundamentals ν₂, ν₃, and ν₄ and the overtone band 2ν₃. Comparisons are made with the earlier high-resolution measurements on SO₃, and the high correlation among some of the constants related to the Coriolis coupling of the ν₂ and ν₄ levels is discussed in order to understand the areas of disagreement with the earlier work. Splittings of some of the levels are observed and the splitting constant for K=3 of the ground state is determined for the first time. Other observed splittings include the K=1 levels of 2ν₃ (l=2), the K=2 levels of ν₃ and ν₄, and the K=3 levels of ν₂. The analysis shows that there are level crossings between the l=0 and l=2 states of 2ν₃ that allow one to determine the separation of the subband centers for these two states even though access to the l=0 state from the ground state is electric-dipole forbidden. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The l-type resonance constant, q₃, that causes the splitting of the l₃=±1, k=±1 levels of ν₃ also couples the l₃=0 and 2 states of 2ν₃.     

Lifetimes of formaldehyde (A2) in the diffuse region

Lifetimes for the first excited singlet state of H₂CO, D₂CO, and HDCO have been measured from linewidths. In the region of 7000–9000 cm⁻¹ of vibrational energy, lifetimes between 2 and 14 psec were observed. These lifetimes increase with decreasing energy and may be smoothly extrapolated to the results below 4000 cm⁻¹. The H₂CO lifetimes are shorter than D₂CO lifetimes but longer than those for HDCO.     

Optoacoustic laser Stark spectroscopy in the ν2 band of 14NH3

Laser Stark spectroscopy of the R(5, K) transitions in the ν₂ band of ammonia was carried out using coincidences with the 9-μm band CO₂ laser lines. We observed 22 Doppler-free resonances by using an optoacoustic detector and a Lamb-dip stabilized CO₂ laser. A simultaneous analysis of sa, aa, and ss lines yields zero-field transition frequencies with an absolute accuracy of 1 ～ 2 MHz.     

The ν1 and ν3 Bands of the OOO Isotopomer of Ozone

Using 0.002 cm⁻¹ resolution Fourier transform absorption spectra of an ¹⁷O-enriched ozone sample, an extensive analysis of the ν₃ band together with a partial identification of the ν₁ band of the ¹⁷O¹⁶O¹⁷O isotopomer of ozone has been performed for the first time. As for other C_2v-type ozone isotopomers [J.-M. Flaud and R. Bacis, Spectrochim. Acta, Part A 54, 3–16 (1998)], the (001) rotational levels are involved in a Coriolis-type resonance with the levels of the (100) vibrational state. The experimental rotational levels of the (001) and (100) vibrational states have been satisfactorily reproduced using a Hamiltonian matrix which takes into account the observed rovibrational resonances. In this way precise vibrational energies and rotational and coupling constants were deduced and the following band centers ν₀(ν₃) = 1030.0946 cm⁻¹ and ν₀(ν₁) = 1086.7490 cm⁻¹ were obtained for the ν₃ and ν₁ bands, respectively.