High-resolution spectroscopy of the v2 = 2 a ← v2 = 1 s band of 14NH3

Twenty-one transitions of the v₂ = 2 a ← v₂ = 1 s hot band of ¹⁴NH₃ have been observed by an infrared microwave sideband laser spectrometer with an absolute accuracy of 0.00002 cm⁻¹. One hundred and seventeen transitions of the band have been obtained by a Fourier transform infrared spectrometer at a resolution of 0.005 cm⁻¹. A weighted least-squares analysis of these data has been carried out to yield 17 molecular parameters for the v₂ = 2 a state. These parameters reproduce the experimental frequencies with a root mean square deviation of 0.000123 cm⁻¹. To calculate the frequencies to this accuracy it was necessary to take into account the Δ(K − l) = ±3 interaction between the v₂ = 2 a and v₄ = 1 a states.     

High-resolution spectroscopy on the c1Π ← a1Δ transition in NH

The spectrum of the c¹Π, v = 0 ← a¹Δ, v = 0 band of the NH molecule at λ = 324 nm has been investigated under high resolution by laser-induced fluorescence in a molecular beam. From an analysis of the spectra we obtained: the magnetic dipole interaction constants a_N,H and the electric quadrupole constants eQq_1,2 for both electronic states, the improved values for the Λ-doubling constants q_π, q_π^D, and q_π^H for the c¹Π state, and rotational constants for both electronic states up to a third-order centrifugal distortion. Also, the Λ-doubling in the a¹Δ state could be determined.     

Laser stark spectroscopy of the ν2 fundamental band of 15NH3

The ν₂ fundamental band of ¹⁵NH₃ has been observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 38 band constants including the electric dipole moment and its rotational dependence are determined from 416 Stark resonances observed in the present work and three submillimeter lines reported in the literature. The ν₂-band absorption line frequencies in the region 800–1160 cm⁻¹ and their relative absorption intensities are estimated from the band constants.     

The a2ν2 ← sν2 bands of 14NH3 and 15NH3

Numerous transitions belonging to the a2ν₂ ← sν₂ hot bands of ¹⁴NH₃ and ¹⁵NH₃ have been identified and assigned in the long-path Fourier transform spectra of ammonia. The data have been processed to obtain effective molecular parameters for the a2ν₂ states of ¹⁴NH₃ and ¹⁵NH₃.     

High-resolution inverse Raman spectroscopy of the ν1 band of water vapor

The Raman spectrum of the ν₁ band of water vapor at 7 Torr and 296 K, and at 84 Torr and 404 K, has been measured using high-resolution inverse Raman spectroscopy. The frequencies and relative intensities of the observed transitions are compared to a spectral model based on infrared data. Self-broadening coefficients have been determined for 22 lines from J = 0 to J = 8.     

Laser Stark spectroscopy; a case study in the ν2 fundamental band of 14NH3

The ν₂ fundamental band of ¹⁴NH₃ is observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 41 constants including the electric dipole moment and its rotational dependence are determined from 360 Stark resonances observed in the present work and 67 millimeter- and submillimeter-wave inversion and rotation-inversion lines reported in the literature. The rms residual of the fit is 3.1 × 10⁻⁴ cm⁻¹. Field-free transition frequencies of the band in the region 800–1160 cm⁻¹ are calculated from the constants and tabulated together with their estimated uncertainties and relative absorption intensities. Rotational dependence of the electric dipole matrix elements of a C_3v molecule is presented on the basis of the conventional theory of vibration-rotation.     

Infrared spectrum of the Ar-CO complex: observation of the v co = 2 ← 0 band at 4260 cm −1

The spectrum of the weakly-bound van der Waals complex Ar-CO has been observed for the first time in the region of the CO vibrational overtone, using a long-path (180 m) low-temperature (64 K) absorption cell and a Fourier transform infrared spectrometer. The appearance of the spectrum was very similar to that studied previously in the v _co = 1 ← 0 region. However, it was very much weaker, so a detailed analysis was only possible for the relatively uncongested K = 1 ← 0 and 0 ← 1 subbands. The parameters determined here for these sub-bands should help to constrain the C-O bond length dependence of the Ar-CO intermolecular potential in future theoretical models.     

Infrared tunable diode laser spectroscopy of the Δv = 2 band of 7Li127I

The high-resolution infrared spectrum of the Δv = 2 transitions of ⁷LiI has been measured at temperatures near 1050 K. The observations include vibrational transitions ranging from 2-0 to 10-8. The data were fit to a set of Dunham potential constants complete through the a₆ term, from which the Dunham rovibrational constants were calculated. The band centers for the v = 1-0 and v = 2-0 transitions were determined to be 491.17398 ± 0.00026 cm⁻¹ and 976.73042 ± 0.00038 cm⁻¹, respectively.     

Intensities of two-photon transitions in the 2ν2 band of NH3

We determine theoretically all the coincidences between the ¹⁴NH₃ν₂= 0−2 band and the spectrum of two CO₂ lasers; they can be induced either by a small frequency tuning of lasers or by a Stark tuning of molecular levels. For each two-photon transition we report the line intensity, the preferred laser lines and the necessary Stark field or laser tuning. The theoretical line intensities are compared to the results of an optoacoustic Doppler-free experiment.     

High-resolution spectrum of the ν9 band and reinvestigation of the ν8 band of cis-CH3ONO

The infrared spectrum of methyl nitrite CH₃ONO has been recorded at a spectral resolution of 0.003 cm^?1 using a Fourier-transform spectrometer Bruker IFS125HR. The ν₈ band of the cis isomer has been reinvestigated in the 780–880 cm^?1 spectral range to complete the study made by Goss et al. (2004) [3] and to fit the internal rotor splittings. The BELGI-IR program, which enables us to treat an isolated infrared band for asymmetric molecules containing one internal methyl rotor has been used for the analysis and predictions of spectra. Finally 1036 lines (913 A-type and 123 E-type lines for J≤50 and K_a≤28) have been assigned for the cis isomer and fitted with a standard deviation of 0.00047 cm^?1.Furthermore, for the first time, the ν₉ band of cis-CH₃ONO was investigated in the 540–660 cm^?1 spectral range and rather large internal rotation splittings were also observed at higher J values. For the ν₉ band, the effective approach performed with the BELGI-IR program allowed us to analyze and reproduce 682 lines up to J=50 and K_a=18 with a standard deviation of 0.00051 cm^?1. The multiple vibration–rotation–torsion interactions, which are likely to occur between the excited v₉=1 and v₈=1 states and the torsional manifolds are discussed.     

Rotational analysis of the ν2 band of NH2D

High-resolution diode laser spectra and medium-resolution F-T spectra of deuterated ammonia have been obtained in the 700- to 1030-cm⁻¹ region. Out of about 800 lines measured by diode laser spectroscopy, approximately 500 lines have been assigned to the ν₂ transitions of NH₂D. The parameters for the ground and ν₂ states of NH₂D have been derived by the simultaneous analysis of the infrared and microwave data. The standard deviation for the IR data is ∼8 × 10⁻⁴ cm⁻¹. It is shown that the energy levels of NH₂D in the ν₂ state are heavily perturbed by inversion-rotation interaction and that it is necessary to include higher order inversion-rotation interaction terms to obtain a satisfactory fit of the observed data.     

l-Resonance effects in the hot bands 3v 5 ← 2v 5, (v 4 + 2v 5) ← (v 4 + v 5) and (2v 4 + v 5) ← 2v 4 of acetylene

In the infrared spectrum of C₂H₂ around the fundamental v ₅, the hot bands starting from the levels 2v ₅, 2v ₄ and v ₄ + v ₅ have been investigated. From the analysis of about 20 different bands, 40 molecular constants describing the bending modes v ₄ and v ₅ have been derived.     

Infrared diode laser spectroscopy of the ν2 fundamental band of SH3+

The high-resolution absorption spectrum of the ν₂ fundamental band of SH₃⁺ has been observed with the magnetic field modulation technique. The ions were generated in a hollow cathode discharge through a mixture of H₂ and H₂S. The molecular constants in the excited vibrational state are determined through a least-squares fit of the data to a standard symmetric top energy level expression. The anomalous sign of the centrifugal distortion constants is explained by the Coriolis interaction between the v₂ = 1 and v₄ = 1 states.     

High-resolution Fourier transform study of the ν3 fundamental band of trans-formic acid

Using high-resolution Fourier transform spectra of trans-HCOOH recorded at 5.6 μm, we carried out an extensive analysis of the strong ν₃ fundamental band (carbonyl stretching mode) at 1776.83 cm^?1, starting from results of a previous analysis [Weber WH, Maker PD, Johns JWC, Weinberger E. J Mol Spectrosc 1987; 121: 243–60]. As pointed out in the literature, the ν₃ band is significantly perturbed by resonances due to numerous dark bands. We were able to assign series belonging to the ν₅+ν₇, ν₅+ν₉, ν₆+ν₇ and ν₆+ν₉ dark bands, located at 1843.48, 1792.63, 1737.96 and 1726.40 cm^?1, respectively. The model used to calculate energy levels accounts partly for the observed resonances, and enabled us to reproduce most of the observed line positions, within their experimental uncertainties. We also determined absolute line intensities with an accuracy estimated to 15%. Finally, we generated, for the first time, a list of line parameters for the 5.6 μm region of trans-formic acid.     

High-J transitions in the ν2 bands of 14NH3 and 15NH3

The Fourier transform spectra measured using the multiple reflection absorption cell with a path length of 192 m are reported for the high-J transitions of the ν₂ bands of ¹⁴NH₃ and ¹⁵NH₃. More than 400 transitions which have been assigned for the first time in both ¹⁴NH₃ and ¹⁵NH₃ represent nearly 100% extension of the ν₂ data.     

High-resolution spectroscopy of the a4Σ−3/2 − X12Π3/2 system of gold monosulphide in the near infrared

ABSTRACT

We have recorded the a⁴Σ^? _3/2 ? X₁ ²Π_3/2 (0,0), (1,0), and (2,0) bands of gaseous gold monosulphide (AuS) at sub-Doppler resolution in the near-infrared region. The molecules were made in a hollow cathode discharge source by the reaction of sputtered gold with carbonyl sulphide. The high resolution of the laser excitation spectrum enabled the determination of molecular constants describing the rotational and ¹⁹⁷Au hyperfine structure in both states, as well as the spin–rotation interaction in the a⁴Σ^? _3/2 state. The natures of the two electronic states are discussed in the context of the observed hyperfine structure.     

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.