Diode laser absorption spectrum of cold bands of C2HD at 6500 cm

The absorption spectrum of acetylene-d has been observed at high resolution between 6470 and 6630 cm⁻¹ using an external cavity diode laser. Three cold bands have been observed: the strong 2ν₁ band, the weaker ν₁ + ν₂ + 2ν₅ band, and the (ν₁ + ν₃ + ν₅)¹ band, which gains its intensity through Coriolis resonance with 2ν₁. Centers of unblended lines are determined with an accuracy of approximately 10 MHz.     

Highly sensitive absorption spectroscopy of carbon dioxide by ICLAS-VeCSEL between 8800 and 9530 cm

The absorption spectrum of carbon dioxide has been studied between 8800 and 9530 cm⁻¹ by intracavity laser absorption spectroscopy based on a vertical external cavity surface emitting lasers (VeCSEL). Previous laboratory spectra at high resolution were nearly absent in the considered spectral region. Experiments were carried with natural carbon dioxide and with ¹³C enriched carbon dioxide leading to the determination of the rovibrational parameters of a total of 15 very weak vibrational transitions, including two bands of the ¹⁶O¹³C¹⁸O isotopologue. The observed transitions are assigned to components of the 2ν₁ + 3ν₃ triad and of the much weaker 5ν₁ + ν₃ hexad. Our measured line positions are found in excellent agreement with the predictions of the effective Hamiltonians developed for ¹²C¹⁶O₂ and ¹³C¹⁶O₂ but significant deviations were evidenced for the ¹⁶O¹³C¹⁸O minor isotopologue. The relative band intensities within each polyad are also discussed on the basis of the effective Hamiltonian model.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

The Lamb-dip spectrum of the J + 1 ← J (J = 0, 1, 3-8) transitions of HCN: The nuclear hyperfine structure due to H, C, and N

The pure rotational J + 1 ← J transitions, with J = 0, 1, 3-8, of H¹³CN have been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to H, ¹³C, and ¹⁴N. The present observations allow us to provide for the first time the spin-rotation constant of ¹³C and the spin-spin interaction constant S₁₂ (between H and ¹³C) as well as to remarkably improve the quadrupole coupling and spin-rotation constants of ¹⁴N. In addition, a good empirical estimation of C_I(H), based on ab initio calculations, has also been provided. Furthermore, our frequencies together with previous data permit to determine the most accurate ground state rotational parameters known up to now.     

Line broadening and shift coefficients of acetylene at 1550 nm

Pressure broadening and shift coefficients have been measured for the ν₁ + ν₃ band of acetylene, C₂H₂, broadened by N₂, H₂, D₂, air, and the noble gases at 295 K. Coefficients are reported for lines between 6470 and 6612 cm⁻¹ (1512-1546 nm). The pressure broadening coefficients are in general agreement with those reported for other vibrational bands, indicating that they are insensitive to vibrational excitation. The pressure shift coefficients, by contrast, are found to differ substantially among vibrational bands.     

Empirical low energy values for methane transitions in the 5852-6181 cm region by absorption spectroscopy at 81 K

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by direct absorption spectroscopy between 1.62 and 1.71 μm (5852-6181 cm⁻¹) using a newly developed cryogenic cell and a series of distributed feedback (DFB) laser diodes. The minimum value of the measured line intensities is on the order of 3 × 10⁻²⁶ cm/molecule The investigated spectral range corresponds to the high energy part of the tetradecad dominated by the 2ν₃ band for which a theoretical treatment is not yet available. The positions and strengths at 81 K of 2187 transitions were obtained from the spectrum analysis. From the values of the line strength at liquid nitrogen and room temperatures, the low energy values of 845 transitions could be determined. The obtained results are discussed in relation with the previous work of Margolis and compared to the line list provided by the HITRAN database.     

Water vapor absorption line intensities in the 1900-6600 cm region

Water vapor infrared spectra have been measured using the Bruker IFS 120 HR Fourier transform spectrometer at the Physikalisch-Chemisches Institut of the Justus-Liebig-Universität Giessen. Spectra were recorded at pressure-broadening-limited resolution and at room temperature in the range of 1900-6600 cm⁻¹. The use of fully evacuated transfer optics and a White-type multireflection cell made it possible to obtain pressure×pathlength products up to 31.27 mbar×288.5 m. These spectra have previously been used to determine experimental values of rovibrational line positions and upper energy levels of the 2ν₂, ν₁, and ν₃ bands [Mikhailenko SN, Tyuterev VlG, Keppler KA, Winnewisser BP, Winnewisser M, Mellau G, et. al. The 2ν₂ band of water: analysis of new FTS measurements and high-K_a transitions and energy levels. J Mol Spectrosc 1997;184: 330-49] and of the 3ν₂, ν₁+ν₂, and ν₂+ν₃ bands [Mikhailenko SN, Tyuterev VlG, Starikov VI, Albert KK, Winnewisser BP, Winnewisser M, et al. Water spectra in the region 4200-6250 cm⁻¹, extended analysis of ν₁+ν₂, ν₂+ν₃, and 3ν₂ bands and confirmation of highly excited states from flame spectra and from atmospheric long-path observations. J. Mol. Spectrosc. 2002; 213: 91-121].This work presents the intensities of 3769 lines for the weak and medium transitions in the spectral range indicated. These data provide an independent source of experimental information which is complementary to intensity data available in the literature and can thus help to evaluate experimental errors and the reliability of these spectral line parameters.     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.     

High sensitivity ICLAS of H2O in the region of the second decade (11 520-12 810 cm)

The high resolution absorption spectrum of the H₂¹⁸O isotopologue of water has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) with a sensitivity on the order of α_min ∼ 10⁻⁹ cm⁻¹. The 11 520-12 810 cm⁻¹ spectral region corresponding to the 3ν + δ decade of vibrational states, was explored with an ICLAS spectrometer based on a Ti:Sapphire laser. It allowed detecting transitions with an intensity down to 10⁻²⁷ cm/molecule which is about 100 times lower than the weaker line intensities available in the literature, in particular in the HITRAN database.The rovibrational assignment was performed on the basis of the results of variational calculations and allowed for assigning 3659 lines to the H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, HD¹⁶O and HD¹⁸O species, leaving only 1.7% unassigned transitions. A line list including 1712 transitions of H₂¹⁸O has been generated and assigned leading to the determination of 692 rovibrational energy levels belonging to a total of 16 vibrational states, 386 being newly observed. A deviation on the order of 25% has been evidenced for the average intensity values given by HITRAN and the results of variational calculations. Ninety two transitions of the HD¹⁸O isotopologue could also be assigned and the corresponding upper rovibrational levels are given.     

High-resolution infrared spectroscopy of H12C13CD and H13C12CD in the 470–5200 cm−1 spectral region

The fundamental ro-vibrational bands and the 2ν₄?←?GS, 2ν₅?←?GS, 2ν₃?←?GS, ν₄?+?ν₅?←?GS, ν₃?+?ν₄?←?GS, ν₃?+?ν₄?←?ν?₄, ν₃?+?ν₅?←?ν₅, overtone, combination and hot bands of the two rare isotopologues of acetylene H¹²C¹³CD and H¹³C¹²CD have been detected by Fourier transform infrared spectroscopy (FTIR). The analysis of the data has provided very accurate rotational and vibrational parameters for the ground and for the vibrationally excited states.     

Intracavity laser absorption spectroscopy of D2O between 11 400 and 11 900 cm

The weak absorption spectrum of dideuterated water, D₂O, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) between 11 400 and 11 900 cm⁻¹. This spectrum is dominated by the 3ν₁ + ν₂ + ν₃ and the ν₁ + ν₂ + 3ν₃ centered at 11 500.25 and 11 816.64 cm⁻¹, respectively. A total of 530 energy levels belonging to eight vibrational states were determined. The rovibrational assignment process of the 840 lines attributed to D₂O was mostly based on the results of new variational calculations consisting in a refinement of the potential energy surface of Shirin et al. [J. Chem. Phys., 120 (2004) 206] on the basis of recent experimental observations, and a dipole moment surface from Schwenke and Partridge [J. Chem. Phys. 113 (2000) 6592]. The overall agreement between these calculations and the observed spectrum is very good both for the line positions and the line intensities.     

The high-resolution infrared spectrum of pyrrole between 900 and 1500 cm revisited

The Fourier transform gas-phase infrared spectrum of pyrrole, C₄H₅N, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 900-1500 cm⁻¹ spectral region. Four fundamental bands, ν₈(A₁; 1016.9 cm⁻¹), ν₂₃(B₂; 1049.1 cm⁻¹), ν₇(A₁; 1074.6 cm⁻¹), ν₂₀(B₂; 1424.4 cm⁻¹) and the overtone band 2ν₁₆(A₁; 962.7 cm⁻¹) have been analysed using the Watson model. The ν₈ and 2ν₁₆ bands are unperturbed; the ν₇ and ν₂₃ bands are locally perturbed, while the ν₂₀ band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and I^r-representation as well as A-reduction and III^r-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.     

Diode laser spectroscopy of ethylene overtones at 830 nm

A tunable diode laser spectrometer has been employed to examine the 3rd overtone absorption lines of C₂H₄ at around 12 000 cm⁻¹ (830 nm). The spectrometer sources are heterostructure AlGaAs tunable diode lasers operating “free-running”. By the aid of the wavelength modulation spectroscopy with the second harmonic detection technique and a Herriott type multipass cell 63 very weak absorption lines have been observed for the first time, with cross sections as low as 2 × 10⁻²⁶ cm²/mol, equivalent to . The self-broadening coefficient has been measured for one of the most intense lines.     

ICLAS of weak transitions of water between 11 300 and 12 850 cm: Comparison with FTS databases

Very weak water vapor absorption lines have been investigated by intracavity laser absorption spectroscopy (ICLAS) in the 11 335-11 947 and 12 336-12 843 cm⁻¹ spectral regions dominated by the ν₁ + 3ν₂ + ν₃ and ν₂ + 3ν₃ bands, respectively. A detectivity on the order of α_min ∼ 10⁻⁹ cm⁻¹ was achieved with an ICLAS spectrometer based on a Ti: Sapphire laser. It allowed detecting transitions with an intensity down to 5 × 10⁻²⁸ cm/molecule which is about 10 times lower than the weakest line intensities previously detected in the considered region. A line list corresponding to 1281 transitions with intensity lower than 5 × 10⁻²⁶ cm/molecule has been generated. A detailed comparison with the line lists provided by the HITRAN database and by recent investigations by Fourier transform spectroscopy associated with very long multi pass cell is presented. The rovibrational assignment performed on the basis of the ab initio calculations of Schwenke and Partridge, has allowed for determining 176 new energy levels belonging to a total of 16 vibrational states.     

New combination bands in CCH2 around 0.83 μm recorded using FT-ICLAS

Fourier-transform intracavity laser absorption spectroscopy allowed five ¹²C¹³CH₂ Σ⁺-Σ⁺ bands, all from the ground state, to be identified in the 0.83 μm range. Their rotational analysis was performed and rotational constants are provided. Three of these bands, with origins at 11616.9684(18), 11737.2356(14), and 11761.0322(23) cm⁻¹, have never been reported before. Their upper states are assigned to , respectively.     

Weak water absorption lines around 1.455 and 1.66 μm by CW-CRDS

The absorption spectra of water vapor near 1.455 and 1.66 μm have been recorded with a typical absorption sensitivity of 5 × 10⁻¹⁰ cm⁻¹ by using CW-cavity ring down spectroscopy. A series of 18 distributed feed-back (DFB) lasers was used as sources and allowed for the coverage of the 5911.0-5922.5, 5926-5941.8, 5957.0-6121.6, and 6745-7015.6 cm⁻¹ spectral regions. These regions extend to lower and higher energies our previous study of the water spectrum in the important 1.5 μm transparency window [P. Macko, D. Romanini, S.N. Mikhailenko, O.V. Naumenko, S. Kassi, A. Jenouvrier, Vl.G. Tyuterev, J. Mol. Spectrosc. 227 (2004) 90-108]. The line parameters were determined with the help of an interactive least squares multi-lines fitting program which uses a Voigt function as line profile. More than 1900 water lines with intensities ranging between 10⁻²⁸ and 5 × 10⁻²⁴ cm/molecule at 296 K were measured, about 690 of them being reported for the first time. The rovibrational assignment was performed on the basis of previously determined energy levels and of the results of the variational global calculations [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618-4639]. The assignment results were validated by using the Ritz combination principle together with previously reported water transitions. Several new energy levels were determined for the H₂¹⁶O, H₂¹⁷O, and HD¹⁶O isotopologues. The retrieved line lists of the H₂¹⁶O, H₂¹⁷O, H₂¹⁸O, and HD¹⁶O isotopologues are compared with the available calculated and experimental (FTS) databases for water.     

High resolution analysis of the rotational levels of the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states of SO2

A high resolution (0.0018 cm⁻¹) Fourier transform instrument has been used to record the spectrum of an enriched ³⁴S (95.3%) sample of sulfur dioxide. A thorough analysis of the ν₂, 2ν₂ − ν₂, ν₁, ν₁ + ν₂ − ν₂, ν₃, ν₂ + ν₃ − ν₂, ν₁ + ν₂ and ν₂ + ν₃ bands has been carried out leading to a large set of assigned lines. From these lines ground state combination differences were obtained and fit together with the existing microwave, millimeter, and terahertz rotational lines. An improved set of ground state rotational constants were obtained. Next, the upper state rotational levels were fit. For the (0 1 0), (1 1 0) and (0 1 1) states, a simple Watson-type Hamiltonian sufficed. However, it was necessary to include explicitly interacting terms in the Hamiltonian matrix in order to fit the rotational levels of the (0 2 0), (1 0 0) and (1 0 1) states to within their experimental accuracy. More explicitly, it was necessary to use a ΔK = 2 term to model the Fermi interaction between the (0 2 0) and (1 0 0) levels and a ΔK = 3 term to model the Coriolis interaction between the (1 0 0) and (0 0 1) levels. Precise Hamiltonian constants were derived for the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states.     

High sensitivity ICLAS of H2O in the 12,580-13,550 cm transparency window

High-sensitivity Intracavity Laser Absorption Spectroscopy (ICLAS) is used to measure the high resolution absorption spectrum of H₂¹⁸O between 12,580 and 13,550 cm⁻¹. This spectral region covers the 3v+δ polyad of very weak absorption. Four isotopologues of water (H₂¹⁸O, H₂¹⁶O, H₂¹⁷O, HD¹⁸O) are found to contribute to the observed spectrum. Spectrum analysis is performed with the aid of variational calculations and allowed for assigning 1126 lines belonging to H₂¹⁸O, while only 160 H₂¹⁸O lines are included in the HITRAN-2008 database. Altogether, 823 accurate energy levels of H₂¹⁸O are determined from transitions attributed to 26 upper vibrational states, 438 of them being reported for the first time. New information includes energy levels of four newly observed vibrational states of H₂¹⁸O: (2 4 0), (1 4 1), (0 4 2) and (2 3 1) at 13,167.718, 13,212.678, 13,403.71 and 15,073.975 cm⁻¹, respectively. H₂¹⁸O transitions involving highly excited bending states like (1 6 0), (0 6 1), (0 7 1), (1 7 0), (0 9 0) and even (0 10 0) have been identified as a result of an intensity borrowing from stronger bands via high-order resonance interactions. Thirty-six new energy levels of H₂¹⁷O, present with a 2% relative concentration in our sample, could be determined. The rotational structure of the (0 2 3) state of HD¹⁸O at 13,245.497 cm⁻¹ is also reported for the first time.     

Intracavity laser absorption spectroscopy of HDO between 11 645 and 12 330 cm

The weak absorption spectrum of monodeuterated water, HDO, has been recorded by intracavity laser absorption spectroscopy (ICLAS) between 11 645 and 12 330 cm⁻¹. This spectrum is dominated by the ν₂ + 3ν₃ band of HDO at 11969.76 cm⁻¹. A total of 497 energy levels belonging to 12 vibrational states were determined while only 140 levels were previously reported from a recent investigation by Fourier transform spectroscopy in the same spectral region. The rovibrational identification process of the 1378 lines assigned to the HDO isotopologue was mostly based on the results of the accurate variational calculations of Schwenke and Partridge. The overall agreement between these calculations and the observed spectrum is very good. However, strong discrepancies in the calculated line intensities were evidenced in a few cases corresponding to an intensity transfer to a dark state through local resonance interaction.     

Intracavity laser absorption spectroscopy of HDO between 12 145 and 13 160 cm

The high resolution absorption spectrum of monodeuterated water, HDO, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 12 145-13 160 cm⁻¹ region. The achieved sensitivity (noise equivalent absorption on the order of α_min ∼ 10⁻⁹ cm⁻¹) allowed detecting transitions with line strengths as weak as 10⁻²⁷ cm/molecule which is about 50 times lower than the weakest line intensities previously detected in the considered region.The rovibrational assignment of the 1179 lines attributed to the HDO isotopologue was based on the results of the variational calculations of Schwenke and Partridge as well as the recent calculations based on a new HDO potential energy surface refined from the fitting to the available experimental data. The overall agreement between these new calculations and the observed spectrum is very good, the rms deviation of the differences between the calculated and observed energy values being 0.05 cm⁻¹. A set of 304 new experimental HDO energy levels was obtained. In particular, band origins for the (1 2 2), (2 0 2), and (3 1 1) vibrational states, at 12 568.190, 12 644.652, and 12 919.938 cm⁻¹, respectively, and their rotational sublevels are derived for the first time. A detailed HDO database of 1337 transitions was constructed and is provided as Supplementary Material.