The 404.5-nm system of the ReO molecule

Observations on the emission spectrum of ReO in the region 375–870 nm are reported. Five bands of a $\text{ΔΩ}\text{= 0}$ system with (0, 0) band at 404.5 nm have been rotationally analyzed and the principal results for ¹⁸⁷ReO are (in cm^?1) ν₀ = 24 709.90, B′_e = 0.3819, B″_e = 0.4252, ω′_e = 874.8₂, and $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.1}{}_2$. Data on the minor isotopic species ¹⁸⁵ReO are also reported. It is suggested that broad rotational profiles found in bands near 842 nm may be due to nuclear hyperfine structure.     

Analysis of the 2770-Å emission system in I2

A weak emission spectrum of I₂ near 2770 Å is reanalyzed and found to to minate on the A(1u³Π) state. The assigned bands span v″ levels 5–19 and v′ levels 0–8. The new assignment is corroborated by isotope shifts, band profile simulations, and Franck-Condon calculations. The excited state is an ion-pair state, probably the 1g state which tends toward $\text{I}{}^{\mathrm{?}}\text{(}{}^1\text{S) +}\text{I}{}^{\mathrm{+}}\text{(}{}^3\text{P}{}_1\text{)}$. In combination with other results for the A state, the analysis yields the following spectroscopic constants: T″_e = 10 907 cm^?1, $\text{D}$″_e = 1640 cm^?1, ω″_e = 95 cm^?1, $\text{R″}{}_{\mathrm{e}}\text{= 3.06}\text{A}\text{?}$; T′_e = 47 559.1 cm^?1, ω′_e = 106.60 cm^?1, $\text{R′}{}_{\mathrm{e}}\text{= 3.53}\text{A}\text{?}$.     

Resolution of the discrepancies concerning the optical and microwave values for B0 and D0 of the X 3Σg− state of O2

The discrepancies concerning the optical and microwave values of B₀ and D₀ for the X${}^3\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ state of O₂ have been removed by a nonlinear least-squares fit to all of the lines of the O₂, $\text{b}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{-X}{}^3\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ Red Atmospheric bands recorded by Babcock and Herzberg (Astrophys. J., 108, 167, 1948). The resulting values for B₀″ and D₀″ are in excellent agreement with the Raman and microwave values. Improved values are determined for B₁″, D₁″, γ₁″ (spin-rotation), and ?₁″ (spin-spin). Both γ_v″ and ?_v″ increase in magnitude from v″ = 0 to v″ = 1. Improved Dunham Y_i0 and Y_i1 expansion coefficients are determined for the $\text{b}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ state, from which the Rydberg-Klein-Rees potential is constructed.     

The D′ → A′ transition in I2

A detailed vibrational analysis is given for the D′(2g) → A′(2u³Π) transition (3300–3460 Å) in I₂. The assignments include ～ 150 v′-v″ bands in ¹²⁷I₂ and ～100 in ¹²⁹I₂, spanning v′ levels 0–15 and v″ levels 4–30. These bands are mainly red-degraded but include some violet-degraded and line-like features. The analysis is corroborated by Franck-Condon and band profile calculations. The least-squares fit yields the following constants (cm^?1); ΔT_c = 30 340.8, ω′_e = 103.95, ω_eχ′_e = 0.206, ω″_e = 106.1, ω_eχ″_e = 0.81. Anomalous behavior in the vibrational level structure above v″ = 23 makes the extrapolation to the A′ dissociation limit uncertain, so the absolute energies of both states remain ill-defined. However there is a possibility that the D′ state is the state labeled α by King et al. [Chem. Phys. 56, 145–156 (1981)], in which case the energies are known precisely. There is evidence of weak emission from at least two other electronic transitions in this spectral region, probably $\text{D(0}{}^{\mathrm{+}}\text{u) → X(}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{)}$ ($\text{λ}\text{< 3300}\text{A}\text{?}$) and β → A(1u³Π) ($\text{λ}\text{> 3300}\text{A}\text{?}$).     

Rotational analysis of the B3Π(0+) → X1Σ+ band systems of 35Cl35Cl and 35Cl37Cl in the chlorine afterglow emission spectrum

The B³Π(0⁺) → X¹Σ⁺ band system of Cl₂, excited by the recombination of ground state $\text{Cl}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ atoms at total pressures near 2 Torr, has been rotationally analyzed in the range 6300–9900 Å. About 30 bands, with 0 ≤ v′ ≤ 6 and 5 ≤ v″ ≤ 14, were investigated, mostly for both ³⁵Cl³⁵Cl and ³⁵Cl³⁷Cl. The band origins and rotational constants for the B state were obtained with the help of the known constants for the ground state. The principal molecular constants (cm^?1) for the B³Π(0⁺) state of ³⁵Cl³⁵Cl are as follows: T_e′ = 17 817.67(3); ω_e′ = 255.38(3); ω_e′x_e′ = 4.59(1); ω_e′y_e′ = ?0.038(8); D_e′ = 3341.17(14); B_e′ = 0.16313(3); α_e′ = 2.42(3) × 10^?3; γ_e′ = ?5.7(7) × 10^?5. The equilibrium internuclear separation is 2.4311(2) Å. The results of Briggs and Norrish on a transient absorption spectrum of Cl₂ assigned as $\text{0}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{← B}{}^3\text{Π}\text{(0}{}^{\mathrm{+}}\text{)}$ are reinterpreted with the present constants.     

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.     

The rotational spectrum of the X 2Σ+ state of the SrF radical using laser microwave optical double resonance

The pure rotational spectrum of the $\text{X}{}^2\text{Σ}{}^{\mathrm{+}}$ state of the gaseous SrF radical has been measured using microwave optical double resonance (MODR) techniques. The analysis fully confirms the recent dye laser excitation spectrum and rotational assignment of the $\text{B}{}^2\text{Σ}{}^{\mathrm{+}}\text{-X}{}^2\text{Σ}{}^{\mathrm{+}}$ system. Transitions were measured in both the v″ = 0 and v″ = 1 states to give values of B_e″ = 0.250533 cm^?1, α_e″ = 1.546 × 10^?3 cm^?1 and γ″ (spin-rotation) = 2.49 × 10^?3 cm^?1. General qualitative features of MODR in ²Σ⁺ states are treated and suggested improvements for obtaining experimental hyperfine constants are discussed. The more precise ground state constants are merged with the B-X optical analysis to obtain a more accurate set of constants for both states.     

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.     

Analysis of the B′3Σu− → B3Πg (0,0) emission band of molecular nitrogen

The (0,0) band of the $\text{B′}\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}\text{→ B}{}^3\text{Π}{}_{\mathrm{g}}$ emission (Infrared Afterglow) system of molecular nitrogen has been recorded with a resolution of 0.046 cm^?1 and a line position accuracy of 0.007 cm^?1. Six hundred and seventy-two lines are tabulated into a line list for the 1.53 μm (low-resolution) emission feature. Of these, 482 are assigned as members of the 27 branches of the B′ → B transition, while 150 are identified with the 1PG (3,6) band. Molecular constants for the v = 0 levels of the $\text{B′}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}$ and B³Π_g states have been computed and tabulated.     

The D′ → A′ transition in Br2

A vibrational and rotational analysis is presented for the D′ → A′ transition (2800–2950 Å) of Br₂. The analysis includes 11 rotationally analyzed bands for ⁷⁹Br₂ and 3 for ⁸¹Br₂, plus bandheads for 70 additional v′-v″ bands of ⁷⁹Br₂, ⁸¹Br₂, and ⁷⁹Br⁸¹Br. The latter include some violet-degraded and spikelike features at the long-wavelength end of the spectrum, which are interpreted and assigned with the aid of band profile simulations. The assigned features are fitted directly to 14 vibrational and rotational expansion parameters for the two electronic states, from which the following spectroscopic constants are obtained: ΔT_e = 35706 cm^?1, ω′_e = 150.86 cm^?1, ω″_e = 165.2 cm^?1, B′_e = 0.042515 cm^?1, B″_e = 0.05944 cm^?1, $\text{R′}{}_{\mathrm{e}}\text{= 3.170}\text{A}\text{?}$, $\text{R″}{}_{\mathrm{e}}\text{= 2.681}\text{A}\text{?}$. The spectroscopic parameters are used to calculate RKR potentials and Franck-Condon factors for the transition.     

Microwave optical double resonance and continuous wave dye laser excitation spectroscopy of NO2: Rotational assignment of the K = 0−4 subbands of the 593 nm band

A rotational assignment of approximately 80 lines with K_a′ = 0, 1, 2, 3, and 4 has been made of the 593 nm ${}^2\text{A}{}_1\text{→}{}^2\text{B}{}_2$ band of NO₂ using cw dye laser excitation and microwave optical double-resonance spectroscopy. Rotational constants for the ²B₂ state were obtained as A = 8.52 cm^?1, B = 0.458 cm^?1, and C = 0.388 cm^?1. Spin splittings for the K_a′ = 0 excited state levels fit a simple symmetric top formula and give $\text{(?}{}_{\mathrm{bb}}\text{+ ?}{}_{\mathrm{cc}}\text{)}\text{2}\text{= ?0.0483}\text{cm}{}^{\mathrm{?1}}$. Spin splittings for K_a′ = 1 (N′ even) are irregular and are shown to change sign between N′ = 6 and 8. Assuming that the large inertial defect of 4.66 amu Ų arises solely from A, a structure for the ²B₂ state is obtained which gives $\text{r}\text{(NO) = 1.35}\text{A}\text{?}$ and an ONO angle of 105°. Alternatively, weighting the three rotational constants equally gives $\text{r = 1.29}\text{A}\text{?}$ and θ = 118°.     

The electronic isotope shift in the A2Π-X2Σ+ bands of BeH,BeD and BeT

The 0-0, 1-1, 2-2, and 3-3 bands of the A²Π-X²Σ⁺ transition of the tritiated beryllium monohydride molecule have been observed at 5000 Å in emission using a beryllium hollow-cathode discharge in a He + T₂ mixture. The rotational analysis of these bands yields the following principal molecular constants.

$\text{A}{}^2\text{Π:}\text{B}{}_{\mathrm{e}}\text{= 4.192}\text{cm}{}^{\mathrm{?1}}\text{; r}{}_{\mathrm{e}}\text{= 1.333}\text{A}\text{?}$

$\text{X}{}^2\text{Σ:}\text{B}{}_{\mathrm{e}}\text{= 4.142}\text{cm}{}^{\mathrm{?1}}\text{; r}{}_{\mathrm{e}}\text{= 1.341}\text{A}\text{?}$

$\text{ω}{}_{\mathrm{e}}\text{′ ? ω}{}_{\mathrm{e}}\text{″ = 16.36}\text{cm}{}^{\mathrm{?1}}\text{; ω}{}_{\mathrm{e}}\text{′X}{}_{\mathrm{e}}\text{′ ? ω}{}_{\mathrm{e}}\text{″X}{}_{\mathrm{e}}\text{″ = 0.84}\text{cm}{}^{\mathrm{?1}}$

From the pure electronic energy difference (E_Π - E_Σ)_BeT = 20 037.91 ± 1.5 cm^?1 and the corresponding previously known values for BeH and BeD, the following electronic isotope shifts are derived

$\text{ΔE}{}_{\mathrm{e}}{}^{\mathrm{i}}\text{(}\text{BeH}\text{?}\text{BeT}\text{) = ?4.7 ≠ 1.5}\text{cm}{}^1\text{, ΔE}{}_{\mathrm{e}}{}^{\mathrm{i}}\text{(}\text{BeH}\text{?}\text{BeT}\text{) = ?1.8 ≠ 1.5}\text{cm}{}^1$

and related to the theoretical approach given by Bunker to the problem of the breakdown of the Born-Oppenheimer approximation.     

Rotational analysis of the 9613 Å band of CH3D

The 9613 Å band of CH₃D has been photographed under high resolution using a path length of 640 m and a pressure of 593 Torr. The band is parallel in type and a rotational analysis has been carried out. The principal molecular constants for the upper state are:

$\text{T}{}_0\text{= 10404.770 (15)}\text{cm}{}^{\mathrm{?1}}\text{,}\text{B}\text{= 3.68941 (48)}\text{cm}{}^{\mathrm{?1}}$

. A few small (<0.2 cm^?1) rotational perturbations have been found in the excited state levels with K′ = 0 to 4. No transitions have yet been identified to levels with K′ > 4.The possibility of using the 9613 Å band as a means of measuring the $\text{D}\text{H}$ ratio in planetary atmospheres is discussed.     

The 352 nm emission spectrum of difluorodiazirine

Difluorodiazirine fluoresces strongly in the vapor phase showing an extensive band system from about 352 to 451 nm and with no background continuum. The fluorescence is assigned as $\text{A}\text{?}{}^1\text{B}{}_1\text{(nπ}{}^1\text{)-}\text{X}\text{?}{}^1\text{A}{}_1$ and corresponds to the 352 nm absorption system previously studied.The band system is dominated by a progression in ν₁″, the a₁N = N stretching vibration, with ν₄″, the a₁ CF₂ symmetrical deformation vibration, showing a shorter progression.The 0₀⁰ and most others show type B rotational contours but type C bands, involving ν₅″ (a₂), and probably type A bands, involving ν₇″ (b₁) and perhaps ν₆″ (b₁) are also observed.The extremely low intensity of bands involving ν₃″ (a₁) is surprising but there seems to be no reason to doubt the assignment from infrared and Raman data.There is a strong vibrational perturbation affecting some quite strong bands in a region within about 275 cm^?1 of bands 1_n⁰4₀⁰, where n = 0 – 3. The cause of the perturbation is not known.There is no evidence for the emission spectrum consisting of more than one band system.     

Analysis of the Ã1A″ ← X̃1A′ electronic transition in thiocarbonyl chlorofluoride

The visible absorption spectrum of thiocarbonyl chlorofluoride, ClFCS, in the region 5000 to 3000 Å has been observed under conditions of high resolution in the vapor phase and has been assigned to the $\text{A}\text{?}{}^1\text{A″(nπ}{}^1\text{) ←}\text{X}\text{?}{}^1\text{A′}$ and $\text{a}\text{?}{}^8\text{A″(n, π}{}^1\text{) ←}\text{X}\text{?}{}^1\text{A′}$ electronic transitions. All six fundamental modes have been assigned for both the upper and lower singlet electronic states. From the observed splittings of the even-odd quanta of ν₆′ in the spectrum the barrier to inversion in the $\text{A}\text{?}{}^1\text{A″}$ state has been evaluated to be 1556.0 ± 45 cm^?1.     

The Ã1B2-X̃1A1 two-photon fluorescence excitation spectrum of 1,3-difluorobenzene

The $\text{A}\text{?}{}^1\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ system of 1,3-difluorobenzene has been observed using the technique of two-photon fluorescence excitation obtained with a pulsed dye laser. Calibration was achieved by a combination of the neon optogalvanic spectrum and etalon fringes. In circular, compared to linear, polarization the bands divide into two groups, those which are B₂-A₁ and which retain their intensity with circular polarization, and those which are A₁-A₁ and lose about 60% of their intensity under the same conditions. These two kinds of bands also show characteristic rotational contours. All of the A₁-A₁ bands whose assignments are established obtain their intensity through vibronic interaction in which the vibration ν′₂₅ (ν′₁₄ in the Wilson numbering) mixes the $\text{A}\text{?}$ with, presumably, the $\text{X}\text{?}$ state. There is an important Fermi resonance between the 9¹ and 10¹11¹ levels. Parts of the one-photon absorption spectrum have been photographed to identify sequences associated with the 0₀⁰ band for comparison with those observed in the two-photon spectrum, and to search for bands involving odd quanta of b₂ vibrations, including ν′₂₅ (ν′₁₄); none was found.     

A spectrum of rhenium oxide

The arc emission spectrum of the ReO molecule has been photographed in the region 590–860 nm and three bands of a single electronic transition have been rotationally analyzed. The separation of lines of the isotopic molecules ¹⁸⁵ReO and ¹⁸⁷ReO leads to the conclusion that the vibrational assignments for these bands are 1-0, 0-0, and 0–1. It is conceivable that an electronic isotope shift of ～0.08 cm^?1 exists. The following vibrational and rotational data (cm^?1) have been determined: ν₀(0-0) = 14 038.42, $\text{Δ}\text{G′(}\text{1}\text{2}\text{) = 867.85}$, $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.14}$; B′_e = 0.3889, α′_e = 0.0019, B″_e = 0.4257, α″_e = 0.0043. It is concluded that Λ′ ? Λ″ = +1 with Λ″ ≥ 2.     

The 370-nm electronic spectrum of tropolone: Evidence from single vibronic level fluorescence spectra regarding the assignment of some vibrational fundamentals in the X̃ and à states

Single vibronic level fluorescence (SVLF) spectra of tropolone from vibronic levels in the $\text{A}\text{?}{}^1\text{B}{}_2$ electronic state, in combination with recently reported supersonic jet spectra, have enabled the assigning of many absorption bands in the region of 0₀⁰ which had previously been impossible. Some of the complexity in these bands has been shown to be due to a large Duschinsky effect involving the two lowest b₁ vibrations, ν₂₅ and ν₂₆. It has been shown that these vibrations have wavenumbers of 176 and 110 cm^?1, respectively, in the $\text{X}\text{?}$ state, and 172 and 39 cm^?1 in the $\text{A}\text{?}$ state. This last value shows how unresistent the molecule is in the $\text{A}\text{?}$ state to out-of-plane bending in the region of the five-membered ring. Other aspects of the vibrational complexity are due to the effect of ν′₂₆ in increasing the barrier to tunnelling of the hydrogen-bonding proton in the $\text{A}\text{?}$ state contrasting with very little effect of ν″₂₆ in the $\text{X}\text{?}$ state.     

The magnetic rotation spectrum of iodine monobromide

The MRS of IBr in the visible region of the spectrum has been studied at high resolution and a rotational and vibrational analysis is reported. The spectrum consists of short runs in J′ for several neighboring vibrational states of the mixed B, ${}^3\text{Π}{}_0{}^{\mathrm{+}}$, and $\text{B}\text{?}\text{′}$, 0⁺ electronic states. These results imply that only a small number of closely related rotational-vibrational states of the combined system have sufficiently long lifetimes to provide the sharp lines required for the appearance of a MRS. The values observed extend to higher energies similar results reported by Selin for the absorption spectrum.     

Doppler-limited dye laser excitation spectroscopy of HCF

The cw dye laser excitation spectrum of the $\text{A}\text{?}{}^1\text{A″(000) ←}\text{X}\text{?}{}^1\text{A′(000)}$ vibronic band of HCF was observed between 17 188 and 17 391 cm^?1 with the Doppler-limited resolution, 0.04 cm^?1. The HCF molecule was produced by the reaction of discharged CF₄ with CH₃F, and 853 lines were observed, of which 516 transitions were assigned to K′_a ← K″_a = 3 ← 4, 2 ← 3, 1 ← 2, 0 ← 1, 1 ← 0, 2 ← 1, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 2 ← 0, and 0 ← 2 subbands. A rotational analysis yielded the rotational constants and quartic and sextic centrifugal distortion constants for both the $\text{A}\text{?}$ and $\text{X}\text{?}$ states and the band origin, with good precision. The molecular constants determined reproduce the observed transition frequencies with an average deviation of 0.0038 cm^?1. Small rotational perturbations in the excited state were found at J = 5, 6 and J = 10, 11 of J_1,J and at J = 15, 16 of J_2,J?1 levels.