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, $\text{R′}{}_{\mathrm{e}}\text{= 3.53}\text{A}\text{?}$.     

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) ($\text{λ}\text{> 3300}\text{A}\text{?}$).     

The emission spectra of H35Cl+, H37Cl+, D35Cl+, and D37Cl+ in the region 2700–4100 Å

The $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}\text{-X}{}^2\text{Π}$ emission spectrum of HCl⁺ has been measured and analyzed for four isotopic combinations. These analyses extend previous work and provide rotational constants for the v = 0–2 levels of the ground state and for the v = 0–9 levels of the excited state. RKR potentials have been determined for both states, although the upper state could not be fitted precisely to such a model. Calculated relative intensities based on these potentials demonstrated that the electronic transition moment must change rapidly with lower state vibrational quantum number. Although considerable caution should be exercised in applying the concept of equilibrium constants to the $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}$ state, the following are the best estimates of these constants (in cm^?1) for the $\text{X}{}^2\text{Π}$ state of H³⁵Cl⁺: B_e = 9.9406, ω_e = 2673.7, A_e = ? 643.7, and $\text{r}{}_{\mathrm{e}}\text{= 1.315}\text{A}\text{?}$. For the $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}$ state of H³⁵Cl: T_e = 28 628.08, B_e ～ 7.505, ω_e ～ 1606.5, and $\text{r}{}_{\mathrm{e}}\text{= 1.514}\text{A}\text{?}$.     

Determination of molecular constants of nitric oxide from (1-0), (2-0), (3-0) bands of the 15N16O and 15N18O isotopic species

The (1-0), (2-0), and (3-0) transitions of ¹⁵N¹⁶O and ¹⁵N¹⁸O are investigated. The wavenumbers of the rotation-vibration lines are reported for the overtone bands and the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (1-0) subband. It is shown that in the data reduction it is advantageous to calculate first merged spectroscopic constants ignoring the Λ-type doubling. The vibrational constants ω_e, ω_ex_e, ω_ey_e and the vibrational dependence of the rotational constants are determined. The study of ¹⁵N¹⁸O allows the determination of the equilibrium values of the centrifugal distortion correction A_De to the spin-orbit constant and of the spin-rotation constant γ_e from the isotopic invariance of the ratios $\text{A}{}_{\mathrm{<mtext>De</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}$ and $\text{γ}{}_{\mathrm{<mtext>e</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}$. It is found that $\text{A}{}_{\mathrm{<mtext>De</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}\text{= (?3.9 ± 1.3) × 10}{}^{\mathrm{?6}}$ and $\text{γ}{}_{\mathrm{<mtext>e</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}\text{= (?4.00 ± 0.05) × 10}{}^{\mathrm{?3}}$.     

On the electronic spectrum of the Mo2 molecule observed after flash photolysis of Mo(CO)6

Absorption and emission spectra of Mo₂ were investigated using flash photolysis of the Mo(CO)₆ molecule. Tentative vibrational and rotational analyses of the ⁹⁸Mo₂ spectra were performed. For the ground state, ${}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ type was proposed with ω_e = 477.1 cm^?1, $\text{r}{}_{\mathrm{e}}\text{= 1.929}\text{A}\text{?}$, and D₀(Mo₂) = 95 ± 15 kcal mole^?1. The results were compared with theoretical calculations for Mo₂ and experimental results for Cr₂ obtained previously. It seems reasonable that the transition metal diatomic molecules of this type have a high bond order.     

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 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.     

Infrared bands of 12C2HD

The rotational structure of about 40 bands of ¹²C₂HD observed in the region 6000?600 cm^?1 has been measured and interpreted with the purpose of determining a comprehensive set of molecular constants for this isotopic variety of acetylene. Combining these data with the results for ¹²C₂H₂ and ¹²C₂D₂, a reevaluation of the equilibrium internuclear distances for the acetylene molecule has been made: $\text{r}{}_{\mathrm{e}}\text{(CH) = 1.06215 ± 17 × 10}{}^{\mathrm{?5}}\text{A}\text{?}$ and $\text{r}{}_{\mathrm{e}}\text{(CC) = 1.20257 ± 9 × 10}{}^{\mathrm{?5}}\text{A}\text{?}$ were obtained. This paper presents all the molecular constants derived in this study.     

Polarization spectroscopy of the E0g+-B0u+ band system of Br2

The E-B (0_g⁺-0_u⁺) band system of Br₂ has been investigated at Doppler-limited resolution using polarization labeling spectroscopy. Merged E state data for the three naturally occurring isotopes in the range v_E = 0–16, expressed in terms of the constants for ⁷⁹Br₂, are (in cm^?1) Y_0,0 = 49 777.962(54), Y_1,0 = 150.834(22), Y_2,0 = ?0.4182(28), Y_3,0 = 6.6(11) × 10^?4, Y_0,1 = 4.1876(28) × 10^?2, Y_1,1 = ?1.607(16) × 10^?4, and Y_0,2 = 1.39(39) × 10^?8. The bond distance is $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{= 3.194}\text{A}\text{?}$, and the diabatic dissociation energy to $\text{Br}{}^{\mathrm{+}}\text{(}{}^3\text{P}{}_2\text{) +}\text{Br}{}^{\mathrm{?}}\text{(}{}^1\text{S}{}_0\text{)}\text{is 34 700 cm}{}^{\mathrm{?1}}$.     

Fourier spectrometry: Rovibrational analysis of an infrared 1Π → 1Σ system of yttrium monoiodide

The infrared spectrum of yttrium monoiodide has been excited in an electrodeless microwave discharge and explored between 2500 and 12 000cm^?1 with a high-resolution Fourier transform spectrometer. A unique system is observed (ν₀₀ = 9905.520 cm^?1), which we attribute to a ${}^1\text{Π}\text{→}{}^1\text{Σ}$ transition and an extensive analysis is made. Rovibrational constants are obtained for both states mainly from a simultaneous multiband fitting. This procedure is applied to the whole set of 2231 observed line wavenumbers in the 1-0, 0-0, and 0–1 bands, yielding a final weighted standard deviation of 0.0038 cm^?1. Furthermore, a partial analysis of the 2-0 and 3-1 bands is performed. The following equilibrium constants are derived (cm^?1):

$\text{ω′}{}_{\mathrm{e}}\text{=192.210 ω′}{}_{\mathrm{e}}\text{x′}{}_{\mathrm{e}}\text{=0.463}$

$\text{B′}{}_{\mathrm{e}}\text{=0.0399133 α′}{}_{\mathrm{e}}\text{=0.0001150}$

$\text{ω″}{}_{\mathrm{e}}\text{=215.815 ω″}{}_{\mathrm{e}}\text{x″}{}_{\mathrm{e}}\text{=0.514}$

$\text{B″}{}_{\mathrm{e}}\text{=0.0422163 α″}{}_{\mathrm{e}}\text{=0.0001125}$

High-order constants D_v and H_v are also calculated for the various vibrational levels (v′ = 0, 1, 2, 3; v″ = 0, 1).     

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.     

Measurement and interpretation of the 1-0 band of 14N16O at 1900 cm−1

The wavenumbers of the vibration rotation band lines of ¹⁴N¹⁶O are reported for the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ subbands of the 1-0 transition in the infrared. The full set of spectroscopic constants for this band has been determined by direct approach using the analysis of Zare, Schmeltekopf, Harrop, and Albritton. In addition to the band origin ν₀ and the B, D, H constants for the lower and upper vibrational levels, the following spin-orbit coupling constants have been derived: $\text{A}\text{?}{}_0\text{= 123.02772 ± 0.00011}$ and $\text{A}\text{?}{}_1\text{= 122.78248 ± 0.00011}$ (in cm^?1). Apparent centrifugal corrections to these constants have been determined and the values obtained for them are $\text{A}\text{?}{}_{\mathrm{<mtext>D</mtext><mtext>0</mtext>}}\text{= (0.347573 ± 0.00051) × 10}{}^{\mathrm{?3}}$ and $\text{A}\text{?}{}_{\mathrm{<mtext>D</mtext><mtext>1</mtext>}}\text{= (0.337135 ± 0.00050) × 10}{}^{\mathrm{?3}}\text{cm}{}^{\mathrm{?1}}$. Λ-Type doubling constants evaluated by using both grating and tunable laser data are also reported.     

Revised molecular constants,RKR potential,and long-range analysis for the B3Π(0u+) state of Cl2, and rotationally dependent Franck-Condon factors for Cl2 (BX1Σg+)

Literature data for the line frequencies of the B³Π(0_u⁺) ← X¹Σ_g⁺ transition of Cl₂ are fitted directly by least squares to obtain new molecular constants. The constants from individual bands are merged to obtain single-valued estimates of the rotational constants for each vibrational level of the B state. The results are combined with recent data from the B → X system in emission to obtain new RKR turning points for the B and X states, and Franck-Condon factors for the B-X system. The new constants are also used to provide revised long-range parameters for Cl₂(B) which differ from those of earlier work. In particular, the coefficient C₅ of the leading term in the inverse-power long-range potential is now found to be $\text{C}{}_5\text{= 1.16(2) × 10}{}^5\text{A}\text{?}{}^5\text{cm}{}^{\mathrm{?1}}$. Theoretical results for the variation of centrifugal distortion parameters for levels near dissociation are tested for D_v and H_v, and an extrapolation based on this behavior is used to facilitate determination of reliable B_v and G(v) values for the highest observed B-state levels.     

The 2880-Å emission spectrum of I2: Ion-pair states near 47 000 cm−1

An emission system of I₂ in Ar in the region 2830–2890 Å is examined under high resolution and found to display fine violet-degraded band structure. This system is interpreted as a charge-transfer transition originating from an ion-pair state near 47 000 cm^?1 and terminating on a weakly bound state which dissociates to two ground-state atoms. This interpretation is supported by spectral simulations employing a bound-free model. The transition is tentatively assigned as $\text{0}{}_{\mathrm{<mtext>g</mtext>}}{}^{\mathrm{?}}\text{→ 2431 0}{}_{\mathrm{<mtext>u</mtext>}}{}^{\mathrm{?}}\text{(}{}^3\text{Π}\text{)}$, according to which the excited state becomes the fourth ion-pair state near 47 000 cm^?1 to be experimentally characterized, and the lower state is the last component of the lowest ³Π state to be identified. The vibrational assignments include about 45 bands in ¹²⁷I₂ and ¹²⁹I₂, spanning v′ = 0–4 and v″ = 6–19, but with the numbering of the lower state remaining uncertain by several units. The main spectroscopic constants for the excited state are T_e = 47 070 cm^?1, ?_e = 105.7 cm^?1, ?_ex_e = 0.49 cm^?1. The spectral simulations place the lower state's potential curve 34 650 cm^?1 below the upper state at R = R′_e, with slope ?850 cm^?1/Å. For our “best” numbering of the lower state, ?_e = 20.5 cm^?1, ?_ex_e = 0.29 cm^?1, T_e = 12 190 cm^?1, and D_e = 360 cm^?1.     

Reexamination of the I2 spectrum near the B(3Π0u+) state dissociation limit

The disagreement of Danyluk and King's (Chem. Phys.25, 343 (1977)) rotational constants for levels lying near the dissociation limit of B-state I₂ with the mechanical behavior predicted by near-dissociation theory is investigated. The discrepancies are shown to be much too large to be explained by either the neglect of centrifugal distortion effects in the original analysis or by rotational or spin-rotation coupling to a nearby repulsive 1_u state. These differences are therefore attributed to experimental error, a conclusion which is confirmed by more recent experimental results. A reanalysis of the best available data for levels near the dissociation limit of B-state I₂ then yields improved values for the B-state dissociation limit $\text{D}$ = 20 043.16 (±0.02) cm^?1 of the vibrational index at dissociation v_$\text{D}$ = 87.32 (±0.04) and of the long-range potential constant $\text{C}{}_5\text{= 2.88 (±0.03) × 10}{}^5\text{cm}{}^{\mathrm{?1}}\text{A}\text{?}{}^5$. This in turn implies a slightly improved ground-state dissociation energy of $\text{D}$₀ = 12 440.18 (±0.02) cm^?1.     

The breakdown of the Born-Oppenheimer approximation for a diatomic molecule: The dipole moment and nuclear quadrupole coupling constants

In the Born-Oppenheimer approximation the dipole moment of the vibrational levels of a ¹Σ electronic state of a heteronuclear diatomic molecule can be expressed as a power series in [$\text{(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v +}\text{1}\text{2}\text{)}$], where v is the vibrational quantum number, and to order $\text{(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)}{}^2$ this expression is

$\text{μ}{}_{\mathrm{v}}\text{=[μ}{}_{\mathrm{e}}\text{+(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)}{}^2\text{μ}{}_{\mathrm{c}}\text{]+μ}{}_1\text{[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]+μ}{}_2\text{(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]}{}^2$

Similarly the nuclear quadrupole coupling constant eQq of each nucleus in the molecule can be expressed as

$\text{eQq=[eQq}{}_{\mathrm{e}}\text{+(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)}{}^2\text{eQq}{}_{\mathrm{c}}\text{]+eQq}{}_1\text{[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]+eQq}{}_2\text{(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]}{}^2$

In this paper the effect of the breakdown of the Born-Oppenheimer approximation on the expressions for μ_v and eQq for an isolated ¹Σ ground electronic state of a heteronuclear diatomic molecule is determined. The effect is to change only μ_c and eQq_c and, therefore, to alter the relationship between the μ_v or eQq values of two isotopes of a molecule. The intensities of the lines in the rotation and rotation-vibration spectrum are also slightly modified by this effect.For the HCl molecule we find that

$\text{μ}{}_{\mathrm{v}}\text{=[1.0908+(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(164)]+8.6[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]?9.5[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]}{}^2\text{D}$

where the second term (+164 D) would have the value ?4 D in the Born-Oppenheimer approximation. Similarly for the ³⁵Cl nucleus of the HCl molecule we have

$\text{eQq=[?66.806+(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(2460)]?472.23[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]+750[(}\text{B}{}_{\mathrm{e}}\text{ω}{}_{\mathrm{e}}\text{)(v+}\text{1}\text{2}\text{)]}{}^2\text{MHz}$

where the second term (+2460 MHz) would be ?110 MHz in the Born-Oppenheimer approximation.     

Laser-induced fluorescence of Pb2

Pb₂, which occurs in lead vapor, was studied by the technique of laser-induced fluorescence using single-mode Ar-laser excitation. The fluorescence observed could be classified into the F-X system. Ten progressions involving vibrational quantum numbers v′ = 0?9 and v″ = 0?22 were analyzed. Including collision-induced lines, rotational quantum numbers from J = 25 to J = 300 were observed. The vibrational constants and the numbering of the states had to be reassigned. For the first time rotational constants were determined for the Pb₂ molecule. The internuclear distances of ²⁰⁸Pb₂ in the F and X state are $\text{r = 3.079}\text{A}\text{?}$ and $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{= 2.930}\text{A}\text{?}$, respectively. Using the constants derived RKR potentials and Franck-Condon factors were calculated, which confirmed the vibrational assignments and constants.     

Rotational analysis of the A2Πu-X2Πg Second Negative band system of O2+

Existing high-resolution data for the $\text{O}{}_2{}^{\mathrm{+}}\text{A}{}^2\text{Π}{}_{\mathrm{u}}\text{- X}{}^2\text{Π}{}_{\mathrm{g}}$ Second Negative band system have been analyzed using a nonlinear least-squares fit that employs numerically diagonalized Hamiltonians. Values for the full set of molecular constants of the A²Π_u and X²Π_g states are obtained for the first time. In addition to values for ν₀(v′, v″), B_v, and D_v, the values for the spin-orbit coupling constants A_v are determined for both states. For the X²Π_g state, which is near Hund's case (a), the agreement between these A_v″ values and those predicted by theory is good. However, for the A²Π_u state, which is much nearer to case (b), these A_v′ values and theory disagree both in magnitude and in variation with vibrational level. The A²Π_u state is an inverted state for vibrational levels v′ ≤ 5 and is a regular state for levels v′ = 6–8 (the upper limit of present high-resolution data). Λ-doubling parameters are determined for the X²Π_g state, the only state where Λ-doubling is statistically significant. Spin-rotation interaction is not statistically significant for either state. Dunham Y_i0 and Y_i1 expansion coefficients are determined for each state. Theoretical D_v values calculated from RKR potentials are used to improve the B_v values in the reduction of the data.     

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.     

Analysis of the Raman spectrum of SF6

The Raman active fundamentals ν₁(A1g), ν₂(Eg), ν₅(F2g), and the overtone 2ν₆ of SF₆ have been investigated with a higher resolution and the band origins were estimated to be: ν₁ = 774.53 cm^?1, ν₂ = 643.35 cm^?1, ν₅ = 523.5 cm^?1, and 2ν₆ = 693.8 cm^?1. Raman and infrared data have been combined for estimation of several anharmonicity constants. The ν₆ fundamental frequency is calculated as 347.0 cm^?1. From the analysis of the ν₂ Raman band, the following rotational constants of both the ground and upper states have been calculated:

$\text{B}{}_0\text{= 0.09111 ± 0.00005}\text{cm}{}^{\mathrm{?1}}\text{; D}{}_0\text{= (0.16±0.08)10}{}^{\mathrm{?7}}\text{cm}{}^{\mathrm{?1}}$

;

$\text{B}{}_2\text{= 0.09116 ± 0.00005}\text{cm}{}^{\mathrm{?1}}\text{; D}{}_2\text{= (0.18±0.04)10}{}^{\mathrm{?7}}\text{cm}{}^{\mathrm{?1}}$

.