Fluorescence from the 2B1 state of NO2 excited at 4545 Å

The 4545 Å line of the Ar⁺ laser has been used to excite a ^pR₁ line of a vibrational band of the ²B₁-²A₁ system of nitrogen dioxide. Fluorescence from the upper level to the ground electronic state forms a long progression in the bending vibration. This progression can be followed from v″₂ = 0 up to v″₂ = 12, and the fluorescence intensity passes through several local minima as a function of v″₂. The main features of the intensity distribution can be reproduced using a model Hamiltonian which separates the bending and rotation from the stretching vibrations. This Hamiltonian can also be used to reproduce the fluorescence frequencies by adjusting the potential function of the lower state.     

Theoretical study of the AlO blue-green (B2∑+−X2∑+ band system

Two independent, extensive theoretical calculations are reported for the relative band strengths of the AlO (B²∑⁺?X²∑⁺) blue-green system and for the radiative lifetimes of the lowest few vibrational levels of the B²∑⁺ state. The theoretical lifetimes, which include a small (<0.5%) contribution from bound-bound transitions into the A²Π state, are in excellent agreement with laser fluorescence studies. The theoretical lifetimes increase monotonically and very slowly with increasing vibrational quantum number. The relative band strengths for the blue-green system derived from the two theoretical calculations are in excellent agreement, but differ systematically from the relative band strengths of Linton and Nicholls. Our results suggest that their self-absorption corrections are not large enough, resulting in relative intensities that are too large, especially for the weak bands with r centroids less than 1.5Å.     

The AB2-XA1 electronic transition of NO2: A rovibronic survey covering 14 300-18 000 cm

More than 250 rotationally resolved vibrational bands of the A²B₂-X²A₁ electronic transition of ¹⁵NO₂ have been observed in the 14 300-18 000 cm⁻¹ range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam techniques. The majority of the observed bands has been rotationally assigned and can be identified as transitions starting from the vibrational ground state or from vibrationally excited (hot band) states. An exceptionally strong band is located at 14 851 cm⁻¹ and studied in more detail as a typical benchmark transition to monitor ¹⁵NO₂ in atmospheric remote sensing experiments. Standard rotational fit routines provide band origins, rotational and spin rotation constants. A subset of 177 vibronic levels of ²B₂ vibronic symmetry has been analyzed in the energy range between 14 300 and 17 250 cm⁻¹, in terms of integrated density and using Next Neighbor Distribution. It is found that the overall statistical properties and polyad structure of ¹⁵NO₂ are comparable to those of ¹⁴NO₂ but that the internal structures of the polyads are completely different. This is a direct consequence of the X²A₁-A²B₂ vibronic mixing.     

Analysis of the ν2 + ν3 band of 12CH4 and 13CH4

The ν₂ + ν₃ bands of ¹²CH₄ and ¹³CH₄ occurring in the region 4400–4650 cm^?1 have been studied from spectra recorded with a high-resolution Fourier transform spectrometer (resolution better than 0.01 cm^?1). Champion's Hamiltonian expansion, Canad. J. Phys.55, 1802 (1977), is applied to the problem of the two interacting F₁ and F₂ vibrational sublevels of this type of a band. As the P branch of ν₂ + ν₃ is strongly overlapped by neighboring bands, a combination-difference method, adapted to tetrahedral XY₄ molecules has been developed to help assignments of lines. A fit of 700 transitions has been performed using 13 new effective constants in the case of ¹²CH₄. In the case of ¹³CH₄, 532 transitions have been fit to 18 constants. The known parameters, relative to the vibrational ground state and the ν₃ state for both methanes, and the ν₂ state for ¹²CH₄ were fixed throughout. Most of the perturbed levels, up to J′ = 12, are well reproduced and the general agreement between experimental and calculated transitions is satisfactory with standard deviations of 0.047 cm^?1 (¹²CH₄) and 0.041 cm^?1 (¹³CH₄). The results (order of magnitude of obtained (ν₂ + ν₃) parameters and comparison of observed and computed intensities) indicate that the ν₂ + ν₃ band is perturbed by many other bands.     

Collisional transfer of rotational energy in the 2B1 electronic state of nitrogen dioxide

Collisional satellite lines have been observed in fluorescence from nitrogen dioxide excited by the 4545-Å line of the argon laser. The 13_0,13 level of the (0, 8, 0) vibrational state is populated by the laser and undergoes collisionally induced transitions to the 11_0,11, 15_0,15, and 17_0,17 states. These collisionally populated states are identified by their fluorescence to the well-studied (0, 0, 0) and (0, 1, 0) levels of the ground electronic state. These satellite lines are also observed in fluorescence to the (0, 2, 0) and (0, 3, 0) vibrational levels of the ground electronic state. The wavenumbers of those lines, together with those from unrelaxed fluorescence and previously published microwave transitions, allow vibrational and rotational constants for the higher vibrational states to be determined more accurately than was previously possible. Several much weaker forbidden transitions have also been observed, including ΔK_a = 0 through ?6 transitions in the (0, 8, 0)-(0, 0, 1) band.     

Rotational analyses and vibrational assignments of the 463- and 474-nm bands of NO2

The excitation spectrum of NO₂ was investigated in the blue region by using a Nd:YAG laser-pumped dye laser. The 463- and 474-nm bands of the ²B₂-²A₁ system were identified and analyzed using the simplification that occurs if the excitation spectrum is monitored at particular wavelengths. Band origins and rotational constants were obtained. Vibrational assignments have been given to these bands by comparing the Franck-Condon Factors calculated for the ²B₂-²A₁ system with the fluorescence intensities of bands going to different vibrational levels of the ground state. The vibrational assignments and molecular constants obtained in this work are (v′₁, v′₂, v′₃) = (3, 11, 0)ν₀(K′ = 0) = 21584.1, $\text{B}\text{= 0.405}$, and $\text{∥}\text{?}\text{′∥ = 0.05}\text{cm}{}^{\mathrm{?1}}$ for the 463-nm band; and (v′₁, v′₂, v′₃) = (2, 12, 0), ν₀(K′ = 1) = 21104.9, $\text{B}\text{= 0.408}$, and $\text{∥}\text{?}\text{′∥ = 0.03}\text{cm}{}^{\mathrm{?1}}$ for the 474-nm band.     

The ν2 + ν4 and 2ν2 isotropic Raman bands of 12CH4

The purely isotropic Raman spectrum of the ν₁ band, the ν₂ + ν₄ band (enhanced through interaction with ν₁), and the 2ν₂ band of ¹²CH₄ was obtained with a spectral resolution of 0.30–0.35 cm^?1 from exposures with different orientations of the linearly polarized exciting light. The ν₂ + ν₄ and 2ν₂ bands show partially resolved rotational structure. The spectra are interpreted in terms of a model which takes explicitly into account vibrational and rovibrational interactions with other vibrational states, using molecular constants determined primarily from infrared spectra. The computed contours are in excellent agreement with the experimental ones and the observed and calculated peak wavenumbers agree within one tenth of the spectral resolution limit, except for a small region near the ν₁ band. The good overall agreement represents an independent check on the overall correctness of the previously reported molecular constants. A detailed discussion is given of the contributions to the intensities of individual transitions from the three transition moment matrix elements, which in an isolated-band model are the intensity parameters of the ν₁, 2ν₄, and 2ν₂ isotropic bands, respectively.     

Jet Spectroscopy of theD12B1–D01B1Transition of thep-Cyanobenzyl Radical

We have generated thep-cyanobenzyl radical in supersonic free expansion, and measured the vibrationally and rotationally resolved laser induced fluorescence (LIF) excitation spectra and the LIF dispersed spectra from the single vibronic levels (SVL) in the green-blue region. The lowest energy band at 20 738 cm⁻¹with the strongest intensity in the excitation spectrum has been assigned to the 0⁰₀band of the visible spectrum, on the basis of the vibronic structures in the SVL dispersed spectra. Based on the band type of the 0⁰₀band,a-type, determined from the rotationally resolved LIF excitation spectrum, we have definitely assigned the visible band to theD₁2²B₁–D₀1²B₁electronic transition. We have found, on the grounds of the vibrational analysis of the dispersed spectra, that the vibronic structure of the 2²B₁–1²B₁electronic transition of the benzyl type is characterized by totally symmetric fundamental modes, 1, 8a, and 9a.     

Diode laser measurements of intensities,N2-broadening,and self-broadening coefficients of lines of the ν2 band of 14N16O2

A diode laser spectrometer (resolution 0.0013 cm^?1) was used to record, in the 12-μm region, high-quality spectra of the ν₂ band of NO₂. Using these spectra, it was possible to obtain the N₂-broadening coefficients and an average self-broadening coefficient from measurements made for seven lines of this band. In addition, 30 single spin-component line intensities were measured. From them, through a least-squares fit, the purely vibrational transition moment of the ν₂ band, as well as two correcting rotational terms involved in the expansion of the transition moment operator, were obtained. These results led to the determination of the dipole moment derivative $\text{?μ}{}_{\mathrm{x}}\text{?q}{}_2\text{= ?0.0604}{}_1\text{± 0.0037}\text{D}$. It was also demonstrated that there is good consistency between the correcting terms deduced from the observed intensities and their theoretical estimates. Finally, a complete spectrum of the ν₂ band of NO₂ was computed, providing a total band intensity S_v(ν₂) = 0.542 × 10^?18cm^?1/molecule cm^?2 at 296 K.     

The absorption spectrum of CO2 around 7740 cm-1

Absolute intensities of the vibration-rotation lines of the CO₂ 401_II←000 band 7734 cm^-1 are measured under high-resolution, low-pressure conditions by use of a White-type 25-m base-path, absorption cell together with a 5-m Czerny-Turner spectrometer. The total band intensity S_B, the purely vibrational transition moment

, and the vibration-rotation interaction constant ζ are calculated from the intensity measurements. The values obtained for these parameters are S_B(401_II) = (7.06±0.07) × 10^-5 cm^-2 atm^-1_293°K,

= (3.08±0.03)×10^-5 debye, and ζ = (2.5±0.5)×10^-4. The intensity of the associated “hot band” 411_II←010 is also determined and found to be S_B(411_II←010) = (0.53±0.02)×10^-5 cm^-2 atm^-1_293°K.     

The B2Σ+-X2Σ+ system of Sr79Br and Sr81Br: Rotational and vibrational analyses

Doppler-free laser polarization spectroscopy has been used to record the (0, 0), (1, 1), and (2, 2) bands of the B²Σ⁺-X²Σ⁺ system for both Sr⁷⁹Br and Sr⁸¹Br. With the help of microwave labeling and additional band selective detection of the laser-induced fluorescence a rotational analysis could be performed. The optical data were combined with the results of independent microwave measurements of the X²Σ⁺ state in a weighted least-squares fit. Local perturbations were observed in each vibrational state of B²Σ⁺. Bandhead positions of Δv = ±1 bands were used for the vibrational analysis.     

New analysis of the ν2, ν3, ν4, and ν6 bands of formaldehyde H2 CO line positions and intensities in the 5-10 μm spectral region

This work, besides its fundamental interest is mainly motivated by the atmospheric importance of formaldehyde. The 10-μm region is indeed a possible spectral domain for the detection of this molecule in the atmosphere and no line parameters are presently available in the atmospheric databases for H₂CO in this spectral range. Using the experimental data available in the literature for the ν₃, ν₄, and ν₆ bands [J. Chem. Phys. 91 (1989) 646 and references therein] and for the ν₂ band [J. Mol. Spectrosc. 96 (1982) 353 and references therein] and adequate theoretical models it proved possible to reproduce satisfactorily the experimental data and to generate a list of line positions and intensities for the 5-10 μm region. The Hamiltonian model accounts for the various Coriolis-type resonances which perturb the energy levels of the 3¹, 4¹, and 6¹ vibrational states as well as for the weaker anharmonic resonances coupling the 2¹ and 3¹ energy levels. This is also the case for the line intensity calculations which allow one to reproduce satisfactorily the line by line intensity measurements as well as the integrated intensities available in the literature.     

New high-resolution analysis of the {ν1 + ν3} band of the NO2 isotopomer of nitrogen dioxide: Line positions and intensities

The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, ¹⁵N¹⁶O₂, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367-377] a new analysis of the ν₁ + ν₃ band located at 2858.7077 cm⁻¹ has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to K_a = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of ¹⁵N¹⁶O₂. Using these parameters and the transition moment operator which was obtained for the main isotopic species, ¹⁴N¹⁶O₂, a comprehensive list of the line positions and intensities was generated for the ν₁ + ν₃ band of ¹⁵N¹⁶O₂.     

Rotational line strengths in the Lyman and Werner bands of H2

Rotational line strengths in the Lyman and Werner bands of molecular hydrogen are affected by the nonadiabatic interaction between the B and C states. Numerical results are presented for the effect of this interaction on relative rotational line strengths for V_x = 0 and V_B ≤ 25, V_c ≤ 9. The B-C interaction is shown to have a pronounced effect for many levels. This difference in rotational line strength factors from the usual Hönl-London factors should be taken into account when relating line oscillator strengths to band oscillator strengths. Relative rotational line strengths are also computed for transitions between C-state levels and excited vibrational levels in the X state. Comparison is made to the measured Werner band emission line intensities of Schmoranzer and Geiger [J. Chem. Phys., 59, 6153 (1973)].     

The laser-induced fluorescence of IBr79

Four fluorescence progressions of the B0⁺-X¹Σ⁺ band of IBr⁷⁹ excited by a single-mode cw dye-laser have been observed and analyzed. Discrepancies in the reported rotational constants of the ¹Σ⁺ state have been resolved and improved vibrational constants determined. A simple method of discriminating between IBr and interfering I₂ fluorescence is described.     

Simultaneous analysis of the ν1, ν4, 2ν2, ν2 + ν5, and 2ν5 infrared bands of 12CH3F

The Fourier-transform spectrum of CH₃F from 2800 to 3100 cm^?1, obtained by Guelachvili in Orsay at a resolution of about 0.003 cm^?1, was analyzed. The effective Hamiltonian used contained all symmetry allowed interactions up to second order in the Amat-Nielsen classification, together with selected third-order terms, amongst the set of nine vibrational basis functions represented by the states ν₁(A₁), ν₄(E), 2ν₂(A₁), ν₂ + ν₅(E), 2ν₅⁰(A₁), and 2ν₅^±2(E). A number of strong Fermi and Coriolis resonances are involved. The vibrational Hamiltonian matrix was not factorized beyond the requirements of symmetry. A total of 59 molecular parameters were refined in a simultaneous least-squares analysis to over 1500 upper-state energy levels for J ≤ 20 with a standard deviation of 0.013 cm^?1. Although the standard deviation remains an order of magnitude greater than the precision of the measurements, this work breaks new ground in the simultaneous analysis of interacting symmetric top vibrational levels, in terms of the number of interacting vibrational states and the number of parameters in the Hamiltonian.     

Experimental determination of the radiative lifetime of the 0, 1, 2, 3 vibrational levels of the B2Σ+ state in CO+

By observing the decay of intensity of vibrational bands of the B²Σ⁺ - X²Σ⁺ and B²Σ⁺ - A²Π_i systems, the lifetimes of the 0, 1, 2, 3 vibrational levels of the B²Σ⁺ state of CO⁺ has been measured. The values are respectively τ=(56.8±1.3), (61.6±0.9), (66.9±2.2) and (70.5±2.9) ns. The variation of the function R_e(r?) cannot be obtained from the lifetime values of the B²Σ⁺ state.     

The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

Rotational analysis and radiative lifetime measurement on the 2B1 (K′ = 0) excited state of NO2 with v′2 = 6, 7, 8, and 9

The rotational structure of the ²B₁ (K′ = 0) subbands of NO₂ with v′₂ = 6, 7, 8, and 9 were analyzed by means of the time-gated excitation spectrum. The excitation spectrum monitored at ν₂, 2ν₂, or 3ν₂ fluorescence band was fairly simplified in comparison to its corresponding absorption spectrum. The band origins and rotational constants are evaluated from the observed data: ν₀ = 20205.0 cm^?1, $\text{B}\text{′ = 0.374}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 6; ν₀ = 21104.4 cm^?1, $\text{B}\text{′ = 0.374}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 7; ν₀ = 22001.9 cm^?1, $\text{B}\text{′ = 0.375}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 8ν₀ = 22898.0 cm^?1, $\text{B}\text{′ = 0.375}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 9. The value of $\text{B}\text{′}$ extrapolated to v′ = 0 is 0.370 cm^?1. This value corresponds to the bond length of 1.19 Å. Fluorescence decays of these excited levels were also studied. Radiative lifetimes obtained by extrapolation to zero pressure from the $\text{1}\text{τ}\text{– P}$ plots were 25–40 μsec. The short-lived excited levels previously reported by some authors were not found.     

Identification and intensities of the “forbidden” 3ν23 band of 12C16O2

Lines of the 3ν₂³ “forbidden” band of ¹²C¹⁶O₂ have been identified in the 2000-cm^?1 region of a long-path, 0.01-cm^?1 resolution laboratory absorption spectrum. This band has detectable intensity due to Δl = 2 Fermi interactions between the upper level and the nearby ν₁ + ν₂ and 3ν₂¹ levels. Intensities of 18 lines of this band have been measured using a nonlinear least-squares spectral fitting technique. The intensities are enhanced at high J and an expression for the intensity distribution as derived by Toth [Appl. Opt.23, 1825–1834 (1984)] is used for the analysis. In terms of the total sample pressure, the vibrational band intensity is 0.194 ± 0.008 × 10^?30 cm^?1/molecule-cm^?2 at 296 K. The coefficient in the F factor is analogous to the Coriolis coefficient ξ and has been determined to be ?0.0413 ± 0.0015. As expected by theory, its value is very close to that of ξ for the related ν₁ + ν₂ band.