Fourier-transform absorption spectroscopy of H2O in the first hexade region

The Fourier-transform absorption spectrum of H₂¹⁸O was recorded in the 6000-7940 cm⁻¹ region and assigned on the base of the very accurate ab initio calculations by Partridge and Schwenke (PS) [J. Chem. Phys. 106 (1997) 4618-4639; J. Chem. Phys. 113 (2000) 6592-6597]. A set of 821 accurate rovibrational energy levels was obtained for six interacting states of the first hexad: (101), (120), (021), (200), (002), and (040). 290 of them are reported for the first time. The experimental line intensities are also estimated and compared with the PS calculations and the available literature data in the considered spectral range.     

High-resolution Fourier-transform spectroscopy of O-enriched water molecule in the 1080-7800 cm region

Fourier-transform absorption spectrum of ¹⁸O enriched water sample was recorded in the 1080-7800 cm⁻¹ region. The transitions of H₂¹⁸O were assigned on the base of the high accuracy ab initio calculations by Partridge and Schwenke (PS). One thousand two hundred and forty-six ro-vibrational energy levels were retrieved, which belong to the , 1, and 1.5 polyads: (0 1 0), (1 0 0), (0 2 0), (0 0 1), (1 1 0), (0 1 1), and (0 3 0) states. Four hundred and thirty-two of them are reported for the first time. The results are also investigated comparing with the PS calculations and the available literature data in the considered spectral range. HD¹⁸O as a small concentration in the sample, more than 4900 transitions were also observed. These transitions yield 1066 ro-vibrational energies of nine vibrational states, 504 energy levels were obtained for the first time.     

HDO absorption spectrum above 11 500 cm: Assignment and dynamics

Assignment of an HDO line list extracted from a recently measured H₂O/HDO/D₂O Fourier transform absorption spectrum recorded in the 11 600-23 000 cm⁻¹ region by Bach et al. (M. Bach, S. Fally, P.-F. Coheur, M. Carleer, A. Jenouvrier, A.C. Vandaele, J. Mol. Spectrosc. 232 (2005) 341-350.) is presented. More than 94% of the 3256 lines are given quantum number assignments and ascribed to line absorption by HDO; most of the remaining lines are actually due to D₂O. High accuracy variational predictions of line positions and intensities are used for the spectral assignment process. Assignments to the ν₁ + 5ν₃, 2ν₂ + 5ν₃, ν₁ + ν₂ + 3ν₃ and ν₁ + 6ν₃ bands are presented for the first time. Comparisons are made with published ICLAS spectra covering the same spectral region and suggestions made for its recalibration. The results are used to illustrate the dynamical behaviour of highly excited vibrational states of HDO and to discuss previous vibrational assignments to high lying rotation-vibration states of this system.     

High-resolution Fourier transform spectrum of H2S in the region of 8500-8900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the polyad. More than 450 transitions were assigned to the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands with the maximum values of quantum numbers J and K_a equal to 14, 7, and 14, 9 for these two bands, respectively. The theoretical analysis was fulfilled with the Hamiltonian which takes into account strong resonance interactions among the studied vibrational states (3 1 0), (2 1 1), and also “dark” states (0 3 2) and (2 3 0). The rms deviation is 0.0019 cm⁻¹. The intensity borrowing effect in the doublets in the P-branch transitions of the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands is observed and discussed.     

Intensity measurements of H2O lines in the spectral region 8000-9350 cm

This paper presents new measurements of H₂¹⁶O lines performed on spectra recorded with the GSMA Fourier Transform Spectrometer (FTS). Our experimental conditions allow one to obtain new line intensity measurements from 10⁻²⁵ to 10⁻²¹ cm/molec at 296 K and self-broadening coefficients in the spectral range centered at 8800 cm⁻¹. In the HITRAN database, data reported for this region is taken from the work of Mandin et al. (1988) [8] and [9] and several articles pointed out problems on the line intensities. We present in this paper some intensity comparisons, first with the HITRAN database, and then with the recent article of Tolchenov and Tennyson (2005) [3]. We finish by a comparison on self-broadening coefficients.     

The continuum absorption in H2O+N2 mixtures in the 2000-3250 cm spectral region at temperatures from 326 to 363 K

The absorption spectra of H₂O+N₂ mixtures, as well, as the spectra of pure gases, have been measured using a Fourier-transform infrared spectrometer at a resolution of 0.1 cm⁻¹. The sample temperatures were 326, 339, 352, and 363 K. Water vapor pressures varied from 8 (60 torr) to 34.5 kPa (259 torr). The nitrogen pressure was kept constant at about 414 kPa (4.1 atm). The path length was 100 m. The continuum absorption coefficients obtained in the spectral range 2000-3250 cm⁻¹ (3.1-5 μm) do not depend significantly on temperature, as is predicted by the well known MT_CKD model. But there are significant deviations in the continuum spectral behavior and magnitude. Around 2050 cm⁻¹ the measured absorption coefficients C_f are about two times larger than those of the model. This deviation grows rapidly at shorter wave lengths, reaching a maximum of two orders of magnitude in the middle of the window at 2500 cm⁻¹. At this point, the deviation starts to decrease significantly and around 3100 cm⁻¹ our results are in agreement with the MT_CKD model. This behavior of the deviation is due to the broad and structureless feature in the region of the nitrogen fundamental band. Most likely, this feature is the N₂ fundamental band component, induced by collisions between H₂O and N₂ molecules. The data obtained and a comparison with the results from the other available sources are presented.     

Fourier transform absorption spectra of H2O and H2O in the 3ν + δ and 4ν polyad region

Fourier transform absorption spectra of H₂¹⁸O-enriched and H₂¹⁷O-enriched water vapor in the 3ν + δ and 4ν polyad region have been analyzed. With the aid of theoretically calculated linelists, we have assigned 1014 lines attributed to H₂¹⁸O and 836 lines of 855 attributed to H₂¹⁷O. Seven new band origins are found for H₂¹⁷O and one for H₂¹⁸O.     

High resolution Fourier transform spectrum of HDO in the 7500-8200 cm region: revisited

The HDO absorption FT spectrum is recorded and analyzed in the 7500-8200 cm⁻¹ spectral region. The high accuracy ab initio calculation of Schwenke and Partridge was successfully applied for spectrum assignment that resulted in derivation of 508 precise rovibrational energy levels for the (3 0 0), (0 3 1), (1 1 1), (0 6 0), (2 2 0), and (0 0 2) states, with 295 of them being reported for the first time. In particular, eight new energy levels, including the band center at 7914.3170 cm⁻¹, were derived for the highly excited bending (0 6 0) state from transitions borrowing their intensities through local high-order resonance coupling with the (3 0 0) and (0 3 1) states.     

Fourier-transform spectroscopy of NNO in the 3500-9000 cm region

The Fourier-transform absorption spectrum of ¹⁵N¹⁴N¹⁶O-enriched nitrous oxide has been recorded at the Doppler limited resolution in the spectral range 3500-9000 cm⁻¹. More than 15 000 transitions of ¹⁵N¹⁴N¹⁶O were observed and assigned based on the global effective Hamiltonian model. The band-by-band analysis led to the determination of the ro-vibrational parameters of a total of 133 bands. Among these bands, 103 were newly observed, and the rotational analysis of 30 others were significantly extended and improved.     

Fourier transform measurements of water vapor line parameters in the 4200-6600 cm region

New high-resolution water vapor absorption spectra were obtained at room temperature in the 4200-6600 cm⁻¹ spectral region by combining Fourier transform spectrometers (FTS) with single and multiple reflection cells. With absorption paths from 0.3 to 1800 m in pure and air diluted water vapor, accurate measurements of about 10400 lines in an intensity range from 10⁻²⁹ to 10⁻¹⁹ cm/molecule have been performed. Positions, intensities, self- and air-broadening coefficients and air-induced shifts were determined for the H₂¹⁶O, H₂¹⁷O, H₂¹⁸O and HDO isotopologues. The rovibrational assignment of the observed lines was performed with the use of global variational predictions and allowed the identification of several new energy levels. One major contribution of this work consists of the identification of 3280 new weak lines. A very close agreement between the new measured parameters and those listed in the database is reported as well as between the observations and the most recent variational calculations for the positions and the intensities. The present parameters provide an extended and homogeneous data set for water vapor, which is shown to significantly improve the databases for atmospheric applications, especially in the transmission windows on both sides of the band centered at 5400 cm⁻¹.     

High-resolution rotational analysis of HDS: 2ν3, ν2 + 2ν3, 3ν3, and ν2 + 3ν3 bands

High-resolution Fourier transform spectrum of the HD³²S molecule was studied in the region of 5000-9000 cm⁻¹. More than 1600 observed transitions yielded 239, 264, 131, and 116 upper state ro-vibrational energies of the states (002), (012), (003), and (013), respectively. With a Watson-type effective Hamiltonian model, the ro-vibrational parameters of these four upper states were determined by a least-square fitting which can reproduce the ro-vibrational energies close to the experimental accuracy. The relative linestrengths are also discussed.     

On the study of high-resolution rovibrational spectrum of H2S in the region of 7300-7900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the v=v₁+v₂/2+v₃=3 poliad. Experimental transitions were assigned to the 3ν₁, 2ν₁+ν₃, ν₁+2ν₃, 3ν₃, 2ν₁+2ν₂, and ν₁+2ν₂+ν₃ bands with the maximum value of quantum number J equal to 11, 14, 10, 11, 8, and 11, respectively. The theoretical analysis was fulfilled with the Hamiltonian model which takes into account numerous resonance interactions between all the mentioned vibrational states. The rms deviation of the reproduction of 510 upper energy levels (derived from more than 1550 transitions) with 75 parameters was 0.0022 cm⁻¹.     

Combined analysis of the high sensitivity Fourier transform and ICLAS-VeCSEL absorption spectra of D2O between 8800 and 9520 cm

The absorption spectrum of dideuterated water, D₂O, has been recorded between 8800 and 9520 cm⁻¹ by intracavity laser absorption spectroscopy (ICLAS) based on a vertical external cavity system emitting laser (VeCSEL) and by high sensitivity Fourier Transform spectroscopy. The combined analysis of the spectra has allowed attributing 1223 transitions to the D₂O species. The spectrum assignment was performed on the basis of the recent results of variational calculations based on an optimized potential energy surface of D₂O. A set of 687 energy levels was derived from transitions assigned to eight upper vibrational states, 577 of them being reported for the first time. A detailed line list has been generated. The line intensities were retrieved mainly from the FTS spectrum and the absolute integrated intensities of the 2v₁ + v₂ + v₃ and the v₂ + 3v₃ bands dominating the spectrum have been determined.     

Line parameters of HDO from high-resolution Fourier transform spectroscopy in the 11 500-23 000 cm spectral region

This work presents new measurements of HDO line parameters in the near-infrared and visible regions (11 500-23 000 cm⁻¹). The measurements consist in high-resolution Fourier transform absorption spectra of H₂O/HDO/D₂O vapor mixtures, obtained using a long absorption path. Spectra with and without nitrogen as the buffer gas were recorded. Due to the simultaneous presence of the three isotopologues H₂O, D₂O, and HDO, the H₂O lines removal and the D₂O lines identification were two necessary preliminary steps to derive the HDO line parameters. The D₂O contribution was small and confined to the well-known 4ν₁ + ν₃ band. An extensive listing of HDO spectroscopic parameters was obtained, for the first time, by fitting some 3256 observed lines to Voigt line profiles. The list contains calibrated line positions, absorption cross-sections and, for many of the lines, N₂-broadening coefficients, as well as N₂-induced frequency shifts. As a result of the low HDO vapor pressures, it was not possible to retrieve the self-broadening parameters. The list is available on the http://www.ulb.ac.be/cpm website.     

High-resolution ro-vibrational spectroscopy of HDO in the region of 8900-9600 cm

The high-resolution absorption spectrum of the HDO molecule was recorded with a Fourier-transform interferometer in the region of 8900-9600 cm⁻¹, where the strongly interacted bands 2ν₁ + ν₃, 3ν₁ + ν₂, ν₁ + 2ν₂ + ν₃, 2ν₁ + 3ν₂, 4ν₂ + ν₃, ν₁ + 5ν₂, and 7ν₂ are located. About 1000 transitions were assigned to these seven bands based on the ab initio predictions [J. Chem. Phys. 106 (1997) 4618]. Altogether, 375 upper energy levels were determined, including 24 energy levels of the highly excited bending (070) state. On that basis, the necessity of the “Effective Hamiltonian” concept in the spectroscopic analysis is discussed.     

High-resolution Fourier transform spectrum of H2S in the region of the second hexade

High-resolution Fourier transform infrared spectrum of was recorded and analyzed in the region of the second hexade . More than 1700 transitions were assigned to the 2ν₁ + ν₂, ν₁ + ν₂ + ν₃, ν₁ + 3ν₂, 3ν₂ + ν₃, 5ν₂, and ν₂ + 2ν₃ bands with the maximum value of quantum number J equal to 18, 18, 13, 11, 13, and 9, respectively. The theoretical analysis was fulfilled with a Hamiltonian model which takes into account numerous resonance interactions between all the vibrational states in this polyad. By a least-square fitting, finally 505 upper energy levels were reproduced by 80 parameters with an rms deviation of 0.0019 cm⁻¹.     

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.     

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.     

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.     

Assignment of surface IR absorption spectra observed in the oxidation reactions: 2H + H2O/Si(1 0 0) and H2O + H/Si(1 0 0)

Infrared reflection absorption spectroscopy that used buried metal layer substrates (BML-IRRAS) and density functional cluster calculations were employed to investigate the water related oxidation reactions of 2H + H₂O/Si(1 0 0)-(2 × 1), 2D + H₂O/Si(1 0 0)-(2 × 1), and H₂O + H/Si(1 0 0)-(2 × 1). In addition to the oxygen inserted coupled monohydrides, which were previously reported in the former reaction system, we report several other oxidized Si hydride species in our BML-IRRAS experiments. Three new pairs of vibrational bands are identified between 900 and 1000 cm⁻¹. These vibrational frequencies were calculated using Si9 and Si10 cluster models that included all possible structures from zero to five oxygen insertions into the top layer silicon atoms using a B3LYP gradient corrected density functional method with a polarized 6-31G** basis set for all atoms. The three pairs of vibrational modes are assigned to the scissoring modes of adjacent and isolated SiH₂ with zero, one, and two oxygen atoms inserted into the Si back bonds. All the other newly observed vibrational peaks related to Si oxidation are also assigned in this study. The Si-O stretching bands observed in the reaction 2D + H₂O/Si(1 0 0)-(2 × 1) show an isotope effect, which suggests that in the system 2H + H₂O/Si(1 0 0)-(2 × 1) also, hydrogen atom tunneling plays an important role for the insertion of oxygen atoms into Si back bonds that form oxidized adjacent dihydrides.