Analysis of High-Resolution Spectra of (18)O(3)

Using a Fourier transform spectrometer, we have recorded the spectra of the (18)O(3) species of ozone in the region 1300-3100 cm(-1), with a resolution of 0.003 cm(-1). The large product pathlength x pressure enable us to record 18 bands, 14 for the first time. The analysis has been performed using effective Hamiltonians for polyads of strongly interacting states for ozone, accounting for Coriolis and anharmonic resonances. The spectral parameters are derived for 16 vibrational states, including the two "dark" states (040) and (130). Various resonances are studied through the mixing coefficients of rovibrational wavefunctions. Systematic intensity measurements allow determination of transition moment parameters for 16 bands. Finally, a complete list of all transitions from 1300 to 3100 cm(-1), with cutoffs 10(-26) cm(-1)/mol cm(-2) (296 K), is calculated. Copyright 2001 Academic Press.     

Experimental Characterization of the Higher Vibrationally Excited States of HCO(+): Determination of omega(2), x(22), g(22), and B(030)

Analyses of high Rydberg series of HCO converging to the (030) vibrational state of the cation establish rovibrational state-detailed thresholds for HCO(+). UV-visible laser double resonance isolates series for assignment. Strongly vertical Rydberg-Rydberg transitions from photoselected N' = 0 and N' = 2 rotational levels of the Sigma(-) Renner-Teller vibronic component of the 3ppi (2)Pi (030) complex define individual series converging to rotational levels, N(+) = 1 through 5 and 3 through 5 of the HCO(+) vibrational states (03(1)0) and (03(3)0), respectively. Extrapolation of autoionizing series locates the positions of these rovibrational states to within +/-0.01 cm(-1). The use of this information combined with precise ionization limits for lower vibrational states determined from earlier Rydberg extrapolations and spectroscopic information available from infrared absorption measurements enables an estimate of the force-field parameters for HCO(+) bending. These parameters include the harmonic bending frequency, omega(2) = 842.57 cm(-1), the vibrational angular momentum splitting constant, g(22) = 3.26 cm(-1), and the diagonal bending anharmonicity, x(22) = -2.53 cm(-1), separated from the off-diagonal contribution, x(12), by reference to ab initio calculations. Results of experiment on the higher vibrationally excited states of HCO(+) are compared with recent theoretical predictions. Copyright 2000 Academic Press.     

HXD中XH拉伸振动的振动跃迁偶极矩方向的理论研究

本文利用局域模研究了“重轻”体系简单分子XH伸缩振动的实验振动光谱. 键偶极方法进一步为实验光谱分析提供了帮助(假设XH伸缩振动的跃迁偶极矩沿着XH键方向排列). 通过局域模和多维简正模对HOD,HND^-,HCD,HSD,HPD^-和HSiD的XH伸缩振动的理论计算, XH伸缩振动的局部1D图片可以用于分析跃迁偶极矩倾斜角度. 在HOD分子中,OH伸缩振动的跃迁偶极矩远离OH键并且向远离OD键的方向倾斜;在HSD,HND^-,HPD^-,HCD和HSiD分子中的XH伸缩振动远离OH键,但朝向OD键,表明键偶极近似法不能很好地适用于“重轻体系”分子,重原子X可以影响跃迁偶极矩方向. 利用分子中原子理论分析了偶极矩的变化.     

The Absorption Spectrum of HDO in the 16 300-16 670 and 18 000-18 350 cm(-1) Spectral Regions

The absorption spectrum of HDO has been recorded by Intracavity Laser Absorption Spectroscopy in the 16 300-16 670 and 18 000-18 350 cm(-1) spectral regions corresponding to the weak 2nu(2) + 4nu(3) and nu(2) + 5nu(3) bands, respectively. The nu(2) + 5nu(3) band centered at 18 208.434 cm(-1) was found almost isolated and has been satisfactorily reproduced in the frame of the effective Hamiltonian model. On the other hand, the 2nu(2) + 4nu(3) band at 16 456.201 cm(-1) is strongly perturbed as the (0 2 4) bright state is involved in a complex interaction scheme including the (1 0 4), (5 0 1), (1 5 2), and (1 11 0) states. The rovibrational assignment of these interacting states was greatly helped by the high-accuracy ab initio predictions performed by D. Schwenke and H. Partridge [J. Chem. Phys. 000-000 (2000)]. They could be partly modeled by an effective Hamiltonian which has allowed the assignment and reproduction of most of the observed transitions. Copyright 2000 Academic Press.     

The High-Resolution FTIR Spectrum of the nu(1) Band of DOBr

Fourier transform infrared spectra of the nu(1) bands of DO(79)Br and DO(81)Br have been recorded with a resolution of 0.0055 cm(-1) in the frequency range of 2510-2800 cm(-1). A total of 1901 lines of the A/B hybrid-type bands of both isotopic species have been assigned and fitted to upper state rovibrational constants employing a Watson's S-reduced Hamiltonian up to sextic terms. The K(a) >/= 4 subband transitions were found to be perturbed and were not included in the fit. The unperturbed band centers for nu(1) of DO(79)Br and DO(81)Br are 2668.79211 +/- 0.00006 and 2668.78842 +/- 0.00005 cm(-1), respectively. The ratio of the vibrational dipole transition moments (μ(a):μ(b)) was found to be 1.30 +/- 0.04 for the band. Copyright 2000 Academic Press.     

High order vibrational matrix elements for diatomic molecules; dipole moment function and transition moments of CO

The fifth and sixth-order contributions to the vibrational matrix elements are obtained for the transitions v→v'(v'?v+4) using an eight power internuclear Dunham potential and a quartic power series expansion of the dipole moment function. The results for the dipole moment coefficients M₀ to M₄ of CO and the transition moments R_v^v' (with v=5, 10, 20) deduced from a calculation including succesively third, fourth, fifth and sixth-order perturbation theory are compared. The validity of these results is discussed.Using a quintic dipole moment function, general expressions for the vibrational matrix elements corresponding to the transitions v→v'(v'? v+5) are also presented and the influence of these contributions on the calculation of the dipole moment coefficients as well as the hot band transition moments of CO is shown.     

Spectroscopy and Intensity Measurements of the 3nu(1)+3nu(3) Tetrad of (12)CO(2) and (13)CO(2)

Three of the four components of the 3nu(1)+3nu(3) tetrad of (12)C(16)O(2) and (13)C(16)O(2), labeled 30031, 30032, and 30033 in HITRAN notation, have been observed by intracavity laser absorption spectroscopy in the 10 450- to 11 000-cm(-1) region. The rotational analysis has yielded the rovibrational parameters of the vibrational states. The experimental values are found to be in very good agreement with the rovibrational energies recently predicted from variational calculations and reduced effective Hamiltonians. The absolute band intensity of these extremely weak transitions have been measured. The study of the relative intensities within the 3nu(1)+3nu(3) tetrad suggests that part of the oscillator strength is carried by the (22(0)3) state. Copyright 2001 Academic Press.     

Rotation of molecular hydrogen in Si: unambiguous identification of ortho-H(2) and para-D(2)

The 3618.4 and 2642.6 cm(-1) infrared absorption lines of interstitial H(2) and D(2) in silicon have been studied under applied uniaxial stresses. The resulting splittings and their small dependence on isotope establish that H(2) in Si is a nearly free rotor and that these lines arise from vibrational transitions between rovibrational states with rotational quantum number J = 1 (T(2) in T(d) symmetry) for ortho-H(2) and para-D(2).     

The absorption spectrum of water between 13 540 and 14 070 cm: ICLAS detection of weak lines and a complete line list

The absorption spectrum of water vapor has been investigated by Intracavity Laser Absorption Spectroscopy (ICLAS) between 13 540 and 14 070 cm⁻¹. This spectrum is dominated by relatively strong transitions of the 4δ polyad of vibrational states. The achieved sensitivity - on the order of α_min ∼ 10⁻⁹ cm⁻¹ - has allowed one to newly measure 222 very weak transitions with intensities down to 5 × 10⁻²⁸ cm/molecule at 296 K. Fifty new or corrected H₂¹⁶O energy levels belonging to a total of 13 vibrational states could be determined from the rovibrational analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the region by Fourier Transform Spectroscopy were critically evaluated and used to construct the best to date set of energy levels accessed by transitions in the considered region. All the rovibrational transitions reaching these upper energy levels and having intensities larger than 4.0 × 10⁻²⁸ cm/mol were calculated. In the resulting line list, the positions at the level of experimental accuracy were augmented with variational intensities leading to the most complete line list for water in normal isotopic abundance in the 13 500-14 100 cm⁻¹ region.     

Frequency and intensity measurements in the fundamental infrared band of HD

The fundamental band of HD has been studied at room temperature and 0.6 atm pressure with a 48-m absorption path and a resolution of 0.01 cm^?1. The frequencies of nine electric dipole and three electric quadrupole transitions were measured with an accuracy of 0.001 cm^?1, and their analysis gives improved molecular parameters for the v = 0 and 1 states of HD. The intensities of the dipole transitions were measured in order to determine the v = 1-0 electric dipole transition moment. These measurements extend earlier experiments to higher J values, thus refining the determination of the rotational dependence of the transition moment.     

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.     

Vibronic spectra of aluminium monochloride relevant to circumstellar molecule

The A^1Π→ X^1Σ^+ transition system of aluminium monochloride is determined by using ab initio quantum chemistry.Based on the multi-reference configuration interaction method in conjugate to the Davidson correction(MRCI + Q), the potential energy curves(PECs) of the three electronic states are obtained. Transition dipole moments(TDMs) and the vibrational energy levels are studied by employing the aug-cc-pwCV5Z-DK basis set with 4220-active space. The rovibrational constants are first determined from the analytic potential by solving the rovibrational Schr ¨odinger equation, and then the spectroscopic constants are determined by fitting the vibrational levels, and these values are well consistent with the experimental data. The effect of spin–orbit coupling(SOC) on the spectra and vibrational properties are evaluated.The results show that the SOC effect has almost no influence on the spectroscopic constants of AlCl molecules. For the A^1Π→ X^1Σ^+transition, the highly diagonalized Frank–Condon factor(FCF) is f(00)=0.9988. Additionally, Einstein coefficients and radiative lifetimes are studied, where the vibrational bands include ν'= 0–19→ν'=0–9. The ro-vibrational intensity is calculated at a temperature of 296 K, which can have certain astrophysical applications. At present, there is no report on the calculation of Al Cl ro-vibrational intensity, so we hope that our results will be useful in analyzing the interstellar Al Cl based on the absorption from A^1Π→ X^1Σ^+.     

Experimental and theoretical study of the ν(HF) absorption band structure in the H2O…HF complex

The νHF absorption band shape of the H₂O…HF complex is studied in the gas phase at a temperature of 293 K. The spectra of H₂O/HF gaseous mixtures in the range 4000–3400 cm^?1 are recorded at a resolution of 0.2–0.02 cm^?1 with Bruker IFS-113v and Bruker IFS-120 HR vacuum Fourier spectrometers in a 20-cm cell. The spectra of the H₂O…HF complex in the region of the ν₁(HF) absorption band are obtained by subtracting the calculated spectra of free H₂O and HF molecules from the experimental spectrum. The ν₁ band of the H₂O…HF complex has an asymmetric shape with a low-frequency head, an extended high-frequency wing, and a characteristic vibrational structure. Two approaches are used to calculate the ν1 band shape as a superposition of rovibrational bands of the fundamental and hot transitions involving the low-frequency modes of the complex. The first approach is based on a simplified semiempirical procedure. The second approach relies on a nonempirical anharmonic calculation of the vibrational energy levels, the frequencies and intensities of the corresponding transitions, and the rotational constants. These parameters are obtained by calculating ab initio the potential energy and dipole moment surfaces in the second-order Möller-Plesset approximation and using the variational method to solve one-, two-, and three-dimensional anharmonic vibrational problems. The absorption spectrum of the complex in the range 3600–3720 cm^?1, reconstructed using the nonempirical electro-optical parameters, reproduces rather well the main features of the experimental spectrum, including the relative intensities of peaks of the vibrational structure. However, the interpretation of most of the structural features of the spectrum differs from that adopted in the semiempirical scheme. First of all, it follows from the results of nonempirical calculation that the central, most intense, maximum of the experimental spectrum should correspond to the v ₁=1←0 transition from the ground vibrational state. This fact gives rise to a new value of the vibrational transition frequency ν ₁ ⁰ in the H₂O…HF complex equal to 3635 cm^?1, which is higher than the commonly accepted value of 3608 cm^?1.     

The nu(1) and nu(3) Bands of the (17)O(16)O(17)O Isotopomer of Ozone

Using 0.002 cm(-1) resolution Fourier transform absorption spectra of an (17)O-enriched ozone sample, an extensive analysis of the nu(3) band together with a partial identification of the nu(1) band of the (17)O(16)O(17)O 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 nu(0)(nu(3)) = 1030.0946 cm(-1) and nu(0)(nu(1)) = 1086.7490 cm(-1) were obtained for the nu(3) and nu(1) bands, respectively. Copyright 2000 Academic Press.     

Direct measurement of a pure rotation transition in H2(+)

The N = 1<--0 pure rotation transition in the nu = 19 level of the ground electronic state of H2(+) was observed at 14,961.7+/-1.1 MHz. Recent theory predicts significant electric dipole intensity in forbidden rotation and rotation-vibration transitions involving levels near the dissociation limit; the relevant levels are bound by only 0.74 and 0.22 cm(-1). The transition was predicted to have a transition moment of 0.42 D; our measurement is consistent with this value.     

Intracavity Laser Absorption Spectroscopy of D2O between 12 850 and 13 380 cm

The high resolution absorption spectrum of dideuterated water, D₂O, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 12 850-13 380 cm⁻¹ spectral region which is the higher energy region reported so far for this water isotopologue. Very high deuterium enrichment was necessary to minimize the HDO absorption lines overlapping the D₂O spectrum. The achieved sensitivity (noise equivalent absorption α_min ∼ 10⁻⁹ cm⁻¹) allowed detecting transitions with line strengths on the order of 5 × 10⁻²⁸ cm/molecule. The spectrum analysis, based on recent variational calculations has provided a set of 422 new rovibrational energy levels belonging to 11 vibrational states, including rotational sublevels for four new vibrational states and one level of the (0 9 1) highly excited bending state. The very weak (1 0 4)-(0 0 0) band at 13 263.902 cm⁻¹, which is the highest D₂¹⁶O band currently observed, could be assigned despite the fact that the HDO absorption in the region is stronger by three orders of magnitude. The list of 996 D₂¹⁶O transitions is provided as Supplementary Material.     

Calculated vibrational transition probabilities of OH(X2Π)

The theoretically derived dipole moment function of OH(X²Π) obtained by Stevens Das, Wahl, Neumann, and Krauss is used to calculate the absolute intensities of the vibrational-rotational transitions of the OH Meinel bands. The calculations take full account of the spin uncoupling and vibration-rotation coupling which markedly influence the radiative transition probabilities. The effect of lambda-doubling on the vibrational transitions is analyzed and generally found to be negligible. Results are tabulated for Δv = v′ – v″ ranging from the fundamental transitions Δv = 1 to the Δv = 5 overtone, for v′ = 1–9 and J′ = 0.5 – 15.5. A comparison is made with available data, and various features of the OH spectrum are examined that are of aeronomical and experimental interest. Thermally averaged emission rates are presented for Δv = 1–5, and the validity of the rotational temperatures commonly derived from experimental intensity distributions is questioned.     

Direct bound-free photodesorption of physisorbed molecules

Because light, weakly adsorbed atoms and molecules have very few bound states, the harmonic oscillator Δv = 1 optical selection rule is invalid for vibrational transitions of the physisorption bond. For such systems, we show that very low power (50 mW) infrared radiation should be sufficient to cause a direct one-photon optical transition from the ground state to continuum translational levels, resulting in photodesorption. Using a simple one-dimensional model, we present computations of the photodesorption rate as a function of photon energy for the Morse potential and several dipole moment functions. The threshold behavior at long wavelengths is analyzed.     

The dipole moment of water: Stark effects in D2O and HDO

The dipole moment of D₂O has been determined from Stark effect measurements for the 3₁₃–2₂₀ and 4₄₁–5₃₂ microwave transitions as 1·857 ± 0·006 and 1·869 ± 0·005D respectively. A rotational dependence of dipole moment has also been established for HDO through μ_a in the 2₂₀–2₂₁ and 5₃₂–5₃₃ transitions; μ_a was determined as 0·662 ± 0·001 and 0·644 ± 0·001D respectively. The total dipole moment for HDO has been determined from the 3₂₁–4₁₄ transition to be 1·85 ± 0·01D and to lie within 0·1° of the bisector of the HOD angle. High resolution Stark spectroscopy has been performed on the 6₂₄–6₁₅ transition of D₂O with improved precision using the 337 μm emission line of the HCN laser. This experiment has confirmed the dipole results from the microwave work and the frequency of the 6₂₄–6₁₅ transition in D₂O has been determined as 890 395 ± 3 MHz.

The slight increase of dipole moment with deuteration is consistent with the dipole moment for H₂O determined from the dielectric constant. This increase is discussed for the vibrational ground state (as for ammonia) in terms of anharmonicity in the bending vibration. The change of μ with rotational transition is interpreted in terms of large changes in molecular geometry for certain rotational states due to centrifugal distortion.     

D2O: ICLAS between 13 600 and 14 020 cm and normal mode labeling of the vibrational states

The high resolution absorption spectrum of dideuterated water, D₂¹⁶O, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 13 600-14 020 cm⁻¹ spectral region which is the highest energy region reported so far for this water isotopologue. Because the HD¹⁶O absorption is stronger by three orders of magnitude in the region under study, it was necessary to use high deuterium enrichment in order to minimize the HD¹⁶O absorption lines overlapping the D₂¹⁶O spectrum. With the high sensitivity achieved (noise equivalent absorption α_min ∼10⁻⁹ cm⁻¹), transitions with line strengths on the order of 5 × 10⁻²⁸ cm molecule⁻¹ could be detected. The spectrum analysis, based on recent variational calculations has provided a set of 177 new rovibrational energy levels belonging to six vibrational states.The most complete set of 53 vibrational energy levels of D₂¹⁶O, including the three newly determined band origins, was constructed from an exhaustive review of the literature data. The fitting of the parameters of the vibrational effective Hamiltonian has allowed to reproduce the whole set of vibrational energies with an rms deviation of 0.055 cm⁻¹. This simple model gave consistent vibrational labels of the D₂¹⁶O states up to 18 000 cm⁻¹. Above 15 000 cm⁻¹, Fermi and Darling-Dennison resonance interaction were found to induce strong vibrational mixings of the wave functions in the normal mode basis, leading to ambiguous vibrational labeling.