Fourier transform and CARS spectroscopy of the ν1 and ν3 fundamental bands of 14NH3

The ν₁ and ν₃ fundamental bands of ¹⁴NH₃ have been measured using the techniques of Fourier transform and coherent anti-Stokes Raman spectroscopy. The effective values of the band origins, rotational and centrifugal distortion constants, and parameters of the vibrational-rotational interactions have been obtained by analyzing these bands as essentially regular parallel and perpendicular bands, with the “off-diagonal” local resonance interactions excluded from the fit. The “diagonal” l-type resonance effects have been included into the analysis of the ν₃ band for the +l, K = 1 and ?l, K = 2 levels.     

Analysis of Coriolis perturbations in the high-resolution infrared spectra of arsine (AsH3)

Numerical methods for the analysis of high-resolution infrared spectra of symmetric top molecules perturbed by Coriolis interactions between degenerate and nondegenerate vibrational levels are discussed in the second order of approximation. Application to the high-resolution infrared spectra of the AsH₃ molecule in the region of the fundamentals ν₁, ν₃ and ν₂, ν₄ yields considerably improved values of the molecular constants of AsH₃, including the band origins rotational constants, Coriolis coupling constants, centrifugal distortion constants, and the parameter of the K-type doubling effect.     

The ν9 + ν11 − ν11, ν10 + ν11 − ν11 hot band system in allene-d4

The hot band system ν₉ + ν₁₁ ? ν₁₁, ν₁₀ + ν₁₁ ? ν₁₁ in allene-d₄ was studied at a resolution near 0.010 cm^?1. About 1500 partly overlapped hot band rotational lines were assigned and fitted to a model taking into account z-Coriolis resonance between the combination levels ν₉ + ν₁₁ and ν₁₀ + ν₁₁ as well as vibrational l-type resonances within these levels. Upperstate constants have been derived from an analysis in which the constants for the ν₁₁ level were constrained. A detailed study of rotational as well as vibrational l-type doublings occurring in the KΔK = ?1 subband is presented, and the sign of vibrational l-type doubling constants for the ν₁₀ + ν₁₁ level is determined. A localized (x, y)-Coriolis resonance between ν₁₀ + ν₁₁ and ν₄(B₁) + ν₁₁ is discussed and the interaction parameter is obtained as well as some constants for ν₄ + ν₁₁.     

The ν7 vibrational states of C3O2: A least-squares fit of the rigid-bender model to the v7ν7l7 energies and rotational constants

The rigid-bender model is used to treat the large-amplitude, low-frequency, bending vibration ν₇ of C₃O₂. Different parameterizations of the bending potential function are considered, and a simple two-term power series is found to give the best fit. With this parameterization, using a least-squares fit to energies and B values, the ν₇ potential function is determined for the ground state as well as for the states in which ν₂, ν₃, ν₄, ν₆, 2ν₆, ν₁ + ν₃, ν₁ + ν₄, ν₂ + ν₃, and 2ν₂ + ν₄ are excited. The excitation of other vibrations has in some cases a drastic effect on the ν₇ potential. In the ground state the potential has a 29 cm^?1 barrier at the linear position, in ν₁ + ν₃ the barrier increases to 79 cm^?1, while in 2ν₂ + ν₄ the barrier vanishes. An equilibrium potential is determined by correcting the ground state potential for the effects of zero-point motion of the normal vibrations ν₁, …, ν₆. This potential has a 35.6-cm^?1 barrier with a minimum at α = 11.14°, where 2α is the angular deviation from linearity. The model accurately predicts the quartic and sextic centrifugal distortion terms for the low-lying v₇ν₇^l₇ states. Second-order l-type coupling is included in the calculations of the quartic terms. The effects of this coupling, which are most pronounced for the ν₇ ≥ 2 states, adequately explain the negative D term recently reported for the ν₂ + 4ν₇⁰ state.     

Diode laser spectrum and analysis of the 882-cm−1 band of s-tetrazine

A high-resolution diode laser spectrum of the 882-cm^?1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10^?5 cm^?1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν₁₂ to ν₁₄.     

Analysis of the Fourier transform spectrum of 13C18O2 in the 4.3- and 16-μm regions

Fourier transform spectra have been obtained for ¹³C¹⁸O₂ in the regions of ν₂ (16 μm) and ν₃ (4.3 μm) at a resolution of 0.04 cm^?1. From a least-squares fit of the P- and R-branch lines for the transitions, values have been calculated for the rotational constants B, the centrifugal distortion constants D, and the band origins. Based on the derived constants, the calculated wavenumbers for the P and R lines of both the 01¹0-00⁰0 and 00⁰1-00⁰0 transitions agree with the observed positions within ±0.003 cm^?1. We have also observed the difference bands ν₁-ν₂ and the hot bands (ν₃ + ν₂) ? ν₂. From an analysis of these transitions we have determined values for the l-doubling constants for ν₂ and the location of the inactive fundamental ν₁.     

Interacting band analysis of the high-resolution spectrum of the 3ν3 manifold of SF6

The two infrared-active vibrational bands of the 3ν₃ manifold of SF₆ have been recorded at T = 160 K with near Doppler-limited resolution using a tunable laser difference-frequency spectrometer. Most of the principal structure has been identified, and over 700 lines with J ≤ 33 have been fitted with a model Hamiltonian which allows the l = 1 and l = 3 subbands to interact. The analysis yields the values of ten spectroscopic constants. When earlier results for the ν₃ band are considered, the values of eight additional constants are derived. The effective harmonic frequency, ω₃⁰, and the three anharmonic coefficients X₃₃, G₃₃, and T₃₃, have been determined with high precision, so that the vibrational levels in the nν₃ ladder can be predicted accurately for several values of n.The Cartesian basis (n_3x, n_3y, n_3z) is found to be the best representation for the vibrational sublevels. Analysis of the rovibrational line strengths reveals that the weak (2, 1, 0) band of 3ν₃ has a very small intrinsic dipole transition moment, so that this band derives most of its intensity by “borrowing” from the strong (3, 0, 0) band.     

Microwave spectrum of methylene fluoride-d2, CD2F2 in the excited vibrational states

The rotational spectra of ¹²CD₂F₂ in the ν₂, ν₃, ν₄, 2ν₄, ν₅, ν₇, ν₈, and ν₉ states were observed and assigned. Weak Coriolis interactions between ν₃ and ν₇, ν₃ and ν₉, and ν₅ and ν₇ were analyzed using approximate expressions for the rotational energy levels. The resonance between the ν₂ and the ν₈ state was found much stronger, and an effective two-dimensional Hamiltonian with the Coriolis term in the off-diagonal block was set up to analyze the spectra. The effect of the Fermi resonance between ν₃ and 2ν₄ was found to be very small.The ground-state spectrum of ¹³CD₂F₂ was observed and the rotational constants and the centrifugal distortion constants were determined. The data on ¹²CD₂F₂ and ¹²CDHF₂ were also improved very much in accuracy.The Coriolis coupling constants and the differences between two vibrational levels in resonance, which were determined by the analysis of the satellite spectra, are in good agreement with those obtained from vibrational spectra, except for the ν₂ band center, which is revised to 1170.3 cm^?1. The force constants were also checked using the centrifugal distortion constants of ¹²CD₂F₂, ¹³CD₂F₂, and ¹²CHDF₂.     

The infrared spectrum of HCCF around 17 μm

The absorption spectrum of HCCF in the region of the CH bending fundamental ν₄ has been studied at a resolution of about 0.03 cm^?1. In addition to the fundamental, the rotational analysis has been performed for six “hot” bands. Several molecular parameters have been derived. The effects of l-type resonances have been discussed. In particular, the influence of the resonance between the sublevels of ν₄ + ν₅ on the effective centrifugal distortion constants has been investigated.     

The rotational spectra of the 79, 69, and 7 vibrational states of nitric acid

The rotational spectra of the first three vibrational states of nitric acid above 1000 cm⁻¹, 7¹9¹, 6¹9¹, and 7², have been measured and analyzed. The 7² state, along with the previously published 7¹ state, show the rotational and centrifugal distortional constants have a near linear dependence on the υ₇ vibrational quantum number. Large changes for several centrifugal distortion constants of the υ₇ = n series of states are attributed to a c-type Coriolis resonance manifold between the ν₇ and ν₆ vibrational modes and the Hamiltonian reduction and representation used to fit the spectra. The 7¹9¹ and 6¹9¹ states have torsional splittings of 12.361(8) and 22.47(1) MHz, respectively. These splittings are large compared to 2.340(8) MHz of the 9¹ state and can be explained by a ∼1-2% mixing through anharmonic Fermi resonances with the 9³ state, which has a large torsional splitting of ∼1760 MHz. The millimeter/submillimeter-wave spectrum of each state was fit separately to the experimental uncertainty of the measurements. The resultant rotational constants, distortional constants and inertial defects agree well with DFT calculations.     

High resolution analysis of the ν12 and ν17 fundamental bands of acrolein, CH2CHCHO, in the 600 cm region

Synchrotron radiation from the new Canadian Light Source facility has been used to obtain a high resolution (0.0012 cm⁻¹) absorption spectrum of acrolein vapor in the 550-660 cm⁻¹ region. Almost 2000 transitions have been included in a detailed analysis of the ν₁₂ (∼564 cm⁻¹) and ν₁₇ (∼593 cm⁻¹) fundamental bands which yielded precise values for the band origins, rotational and centrifugal distortion parameters. The analysis included the a- and b-type Coriolis interactions connecting ν₁₂ and ν₁₇, as well as an a-type Coriolis interaction between ν₁₇ and a “dark” perturbing state, identified as 4ν₁₈. We believe that this is the first high resolution infrared study of acrolein.     

Analysis of some combination-overtone infrared bands of SO3

Several new infrared absorption bands for ³²S¹⁶O₃ have been measured and analyzed. The principal bands observed were ν₁+ν₂ (at 1561 cm⁻¹), ν₁+ν₄ (at 1594 cm⁻¹), ν₃+ν₄ (at 1918 cm⁻¹), and 3ν₃ (at 4136 cm⁻¹). Except for 3ν₃, these bands are very complicated because of (a) the Coriolis coupling between ν₂ and ν₄, (b) the Fermi resonance between ν₁ and 2ν₄, (c) the Fermi resonance between ν₁ and 2ν₂, (d) ordinary l-type resonance that couples levels that differ by 2 in both the k and l quantum numbers, and (e) the vibrational l-type resonance between the A₁^′ and A₂^′ levels of ν₃+ν₄. The unraveling of the complex pattern of these bands was facilitated by a systematic approach to the understanding of the various interactions. Fortunately, previous work on the fundamentals permitted good estimates of many constants necessary to begin the assignments and the fit of the measurements. In addition, the use of hot band transitions accompanying the ν₃ band was an essential aid in fitting the ν₃+ν₄ transitions since these could be directly observed for only one of four interacting states. From the hot band analysis we find that the A₁^′ vibrational level is 3.50 cm⁻¹ above the A₂^′ level, i.e., r₃₄=1.75236(7) cm⁻¹. In the case of the 3ν₃ band, the spectral analysis is straightforward and a weak Δk=±2, Δl₃=±2 interaction between the l₃=1 and l₃=3 substates locates the latter A₁^′ and A₂^′ “ghost” states 22.55(4) cm⁻¹ higher than the infrared accessible l₃=1 E^′ state.     

The vibration-rotation spectrum of methinophosphide: l-Type doubling, l-type resonance and the ν2, 2ν2, and 3ν2 bands of H12CP; The ν1 and ν2 bands of H13CP

The vibration-rotation bands ν₂, 2ν₂, and several “hot” bands of H¹²CP have been recorded and assigned. The states with v₂ = 2, perturbed by l-type resonance and l-type doubling effects have been analyzed on the basis of the existing theory. The energy difference between the 02²0 and the 02⁰0 states was found to be 17.5095 (19) cm^?1. Because of insufficient data, the states with v₂ = 3 could not be corrected for l-type resonance interaction and therefore only an effective l-type doubling constant was obtained. The ν₁ and ν₂ bands of the H¹³CP isotopic molecule (present at natural concentration) were also identified and their spectroscopic constants obtained. The value of I_e for H¹²CP is found to be 25.18793 (26) amu Ų.     

Subject index for volume 100

The ν₂ fundamental band of HNCO has been observed for the first time under a resolution of 0.015 cm^?1. The band origin for this NCO antisymmetric stretching vibration is found to be at 2268.893 cm^?1, rather distant from the previously reported value of 2274 cm^?1. Nineteen subbands have been analyzed and term values for both ground and ν₂ states with K up to 4 have been obtained. Effective rotational constants B and centrifugal distortion constants D and H have also been determined. Interactions are observed with 2ν₄ + ν₅ and ν₃ + ν₄. Large perturbations are observed for K = 0 and K = 1 levels of ν₂. Transitions are also seen for three other vibrations, ν₄ + ν₅ + ν₆, ν₃ + ν₆, and 2ν₄ + ν₆.     

High-resolution Fourier transform study of the perpendicular band ν11 of allene at 353 cm−1

The ν₁₁ perpendicular band of the allene (propadiene) molecule was measured in the region 310–390 cm^?1 on a high-resolution Fourier transform instrument. A total of 1880 lines was assigned to 22 subbands with KΔK values between ?10 and +12. Subband constants which reproduce the observed line positions with standard deviations of 0.0005-0.0008 cm^?1 are tabulated. The strong effects of the two types of l-type interactions allowed for this molecule are included in the Hamiltonian matrix used for the treatment of the spectrum and for the least-squares adjustment of the spectroscopic constants for the ν₁₁ state. A table of the rovibrational energy levels of the ν₁₁ state is given to facilitate analysis of the various hot bands observed throughout the spectrum of allene. Improved estimates are obtained for the elusive rotational constant, A₀, and for the centrifugal constant, D_K⁰, by combining published Raman data for the ν₁₁ band with the new accurate infrared measurements.     

Microwave spectroscopy of OCS in highly excited vibrational states through energy transfer from N2

The efficient vibrational energy transfer between the first excited vibrational state of N₂ and the asymmetric stretching vibrational state of OCS has allowed the observation of many pure rotational lines in different vibrational states of OCS up to 4101 cm^?1: (00⁰1), (01¹1), (02^l1), (10⁰1), (00⁰2), (21¹0), (03^l0), (04^l0), and (05^l0). Accurate values of some rotational, centrifugal distortion and l-doubling constants are determined.     

The microwave spectra and vibration-rotation interaction constants for CD3I in the excited vibrational states

The microwave spectra in the J = 1 → 3 region for CD₃I has been observed and six excited vibrational states assigned. The vibration rotation interaction constants, α^B and nuclear quadrupole coupling constants, eQq, have been determined for the states: ν₂, ν₃, ν₅, ν₆, 2ν₃, and ν₃ + ν₆. For the degenerate vibrational states, the l type doubling constants, q_t were determined.     

Water-vapor absorption spectrum in the 0.59-μm region

The paper gives the results of investigation of the water-vapor absorption spectrum in the range of 586.9–596.6 nm. In the given range, 282 water-vapor absorption lines were recorded and were identified as belonging to the bands 4ν₁ + ν₃, 3ν₁ + 2ν₂ + ν₃, 3ν₁ + 2ν₃. Theoretical justification of the technique for interpreting the observed spectrum was made. The values of more vibration-rotation levels of energy were determined: for state (401) up to J = 10, for state (321) up to J = 10, and for state (302) up to J = 8. The rotational and centrifugal constants of the reduced Watson's Hamiltonian for the vibrational states (401), (321), (302), and (222) and constants of Fermi resonance (401)-(321), (302)-(222), and Coriolis resonance between the states (401), (321), and (302), (222) were determined.     

Microwave study of vibration-rotation spectrum of carbon suboxide C3O2 in the 300- to 1000-GHz frequency range

The submillimeter wave spectrum of the C₃O₂ molecule was investigated within the 300- to 1000-GHz range. The measured frequencies include 256 lines belonging to the ground vibrational state and to four excited vibrational states of ν₇. Rotational and centrifugal constants and constants of “?” splitting for the ground and excited states ν₇¹, 2ν₇², 3ν₇³, 4ν₇⁴ as well as frequencies of purely vibrational transitions ν₇¹ ← 0; 2ν₇² ← ν₇¹; 3ν₇³ ← 2ν₇²; 4ν₇⁴ ← 3ν₇³ together with their correlation matrix were determined.     

Carbon suboxide as a quasilinear molecule with a large amplitude bending mode: Determination of the molecular constants and the ν7 potential function

The model of a quasilinear molecule with a large amplitude bending mode is used to treat C₃O₂. The Hamiltonian operator, including the rotation-vibration interaction, is derived allowing only a single vibrational degree of freedom, namely, the ν₇ mode corresponding to the bending at the central carbon atom. The CCO angle is constrained to be 180°. With this model the rotational energy levels and, thus, the molecular constants can be computed for any ν₇ level once the ν₇ potential is specified. The l-doubling is included only for π states. The model contains three adjustable parameters: the rotational constant in the linear configuration and two terms in the potential function, and these are determined by fitting three experimental quantities: the rotational constants in and the separation between the ground and 2ν7⁰ states. The resulting ν₇ potential has a 30.56 cm^?1 barrier at α = 0 with a minimum at α = 11.04°, where 2α is the angular deviation from linearity. The model gives a good fit to the 2ν₇ Raman data and to the rotational and centrifugal distortion constants in all of the nν7^l states which have been analyzed. A similar analysis is applied with equal success to the states with ν₄, the asymmetric CC stretch mode at 1587 cm^?1, simultaneously excited with a ν₇ mode. The potential in this case has a 56.58 cm^?1 barrier at α = 0 with a minimum at α = 13.02°.