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 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.     

The 2780 Å absorption system of thiophosgene

The vapor phase absorption spectrum of thiophosgene (Cl₂CS) in the 2500–2900 Å region consists of a broad intense band ($\text{log}\text{?}{}_{\mathrm{<mtext>max</mtext>}}\text{= 3.5}\text{at}\text{2540}\text{A}\text{?}$. On the red side of this a vibrationally discrete structure is found which becomes increasingly diffuse and merges into the broad band as the wavelength is decreased. It is shown that this vibrational structure can be explained as due to a $\text{π → π}{}^1$, ${}^1\text{A}{}_1\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ electronic transition between a planar ground state and a pyramidal excited state of the molecule. In the latter state, the CS stretching mode ν₁′(a₁) = 681 cm^?1 and the CCl bending mode ν₃′(a₁) = 147 cm^?1. From the inversion doublet splitting of the out-of-plane mode ν₄′(b₁), the barrier to inversion is calculated to be ～126 cm^?1, with an equilibrium out-of-plane angle of ～20°.     

Dimethyl-s-tetrazine vapor: Visible absorption,laser-excited fluorescence,and photophysics

Except for broader bands, hot bands, and a 500-cm^?1 shift of the 0-0 band to higher frequencies, dimethyl-s-tetrazine as a vapor is found to exhibit the same visible absorption and excited-state zero-level emission spectra that it does when dissolved in p-xylene at 4.2 K and below. Vibrational frequencies in both $\text{A}\text{?}{}^1\text{B}{}_{\mathrm{3u}}$ and $\text{X}\text{?}{}^1\text{A}{}_{\mathrm{g}}$ states show almost no solvent effects. Even an unusual “negative” anharmonicity of the principal progression-forming mode ν_6a in the ground state is the same in both phases. Franck-Condon activity also is independent of phase; in fact, for ν_6a it is the same as for s-tetrazine in the vapor phase. Single vibronic level excitations into the 0-0, 6a₀¹, 1₀¹, and 6a₀² bands show that vibrational relaxation is appreciable for pressures of a Torr and greater. Mode-to-mode flow does not follow the propensity rules exhibited by the S₁ state of benzene. Rotational relaxation and competition of collisional relaxations with predissociation are revealed when foreign gas is added.     

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:

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

;

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

.     

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.     

Laser-excited phosphorescence spectrum of C3S2 in an Ar matrix

The phosphorescence spectrum of C₃S₂ was observed in a low-temperature Ar matrix with excitation of an Ar⁺ laser. The spectrum consists of a very strong 0-0 band at 18 287 cm^?1 and well-resolved progressions in the ν₂, ν₅, ν₆, and ν₇ vibrations. Side bands were found on the high-energy sides of some transitions. The separation between the main and side bands is 23 cm^?1. Polarization analysis suggests that C₃S₂ is linear symmetric in the Phosphorescent state as in the ground electronic state. On the basis of symmetry considerations and a qualitative evaluation of spin-orbit coupling, the phosphorescent state is assigned to ³Σ_u^? with Σ_u⁺ and Π_u components split by spin-spin interaction. The Σ_u⁺ level is lower than the Π_u one by 23 cm^?1 and the main and side band emissions start from the Σ_u⁺ and Π_u levels, respectively. The Σ_u⁺ component seems to acquire allowed character from a ¹Σ_u⁺ state by spin-orbit coupling and from bent ${}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}\text{(}{}^1\text{B}{}_2\text{)}$ and ${}^1\text{Δ}{}_{\mathrm{g}}\text{(}{}^1\text{A}{}_1\text{+}{}^1\text{B}{}_2\text{)}$ states by ν₅ vibronic coupling. Mixing of the Σ_u⁺ and Π_u components through ν₅ is responsible for most of the side bands. The ν₅ frequency is estimated to be 160 ± 20 cm^?1 in the ³Σ_u^? state from the intensities of ν₅ progression bands and from the ground-state frequency, 411 cm^?1.     

The bending vibration bands ν4 and ν5 of HCCI

The bending vibration bands ν₄ and ν₅ of HCCI were studied. From the observed rotational structure the rotational constant B₀ and the centrifugal distortion constant D₀ were obtained. The results were B₀ = 0.105968(7) cm^?1 and D₀ = 1.96(7) × 10^?8 cm^?1 from ν₄ and B₀ = 0.105948(8) cm^?1 and D₀ = 1.96(11) × 10^?8 cm^?1 from ν₅. The structure of the hot bands 2ν₅(Δ) ← ν₅(Π) and 3ν₅(φ) ← 2ν₅(Δ) was also resolved and hence the values α₅ = ?3.033(8) × 10^?4 cm^?1 and q₅ = 9.3(3) × 10^?5 cm^?1 could be derived. The other most intense hot bands following ν₅ could be explained in terms of the Fermi diads $\text{ν}{}_3\text{2ν}{}_5{}^0$ and $\text{ν}{}_3\text{+}\text{ν}{}_5{}^{\mathrm{\pm 1}}\text{3ν}{}_5{}^{\mathrm{\pm 1}}$. Of the numerous hot bands accompanying ν₄, only those between different excited states of ν₄ could be assigned. Then estimates for α₄ and q₄ were also obtained. In addition, several vibrational constants were derived.     

Thioformaldehyde: Rotational analyses of the Ã1A2-X̃1A1 visible absorption system

The $\text{A}\text{?}{}^1\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ electronic absorption spectra of CH₂S and CD₂S have been photographed under high resolution. Selected bands have been rotationally analyzed by least squares line fitting and by band contour methods. Improved rotational constants have been obtained for the ground states of CH₂S and CD₂S by use of combination differences. Bands of all three polarizations appear in the electronic spectrum. The type A origin band is magnetic dipole allowed, whereas the 4₀¹ band is type B. Perturbations are identified in the 0₀⁰ and 3₀¹4₀³ bands of CH₂S. The rotational constant A in the upper state decreases rapidly, in accordance with theoretical calculations, as successive quanta of the inversion mode ν′₄ are excited. The planar inertial defect has a small positive value in the zero level of the upper state although the molecule is slightly nonplanar; the r₈ geometry is $\text{r(}\text{CH}\text{) = 1.082}\text{A}\text{?}$, $\text{r(}\text{CS}\text{) = 1.701}\text{A}\text{?}$, angle HCH = 120°, and the out-of-plane angle is approximately 10°.     

Thioformaldehyde: Vibrational analysis of the Ã1A2-X̃1A1 visible absorption system

The electronic absorption spectra of thioformaldehyde and thioformaldehyde-d₂ have been obtained. A vibrational analysis of the discrete band system in the 6100-4400-Å region is reported. The type A origin bands are at $\text{16 394}\text{16 484}\text{cm}{}^{\mathrm{?1}}$ for $\text{CH}{}_2\text{S}\text{CD}{}_2\text{S}$, and are magnetic dipole allowed. The electronic transition is $\text{A}\text{?}{}^1\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ under the C_2v point group. Most of the intensity of the system is in type B bands, and is due to vibronic mixing with higher ¹B₂ states when the inversion mode ν₄ is excited. The molecule in the excited ¹A₂ state is “floppy-planar,” having a broad potential function with a barrier of the order of 20 cm^?1 to the inversion motion.     

Rotation-vibration analysis of the Coriolis-coupled ν5g, ν6g, ν8g and ν9 bands of H2CCO

Medium resolution infrared grating spectra of gaseous ketene, H₂CCO were recorded between 1000 and 400 cm^?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm^?1 between 450 and 330 cm^?1. The K structure of the fundamentals ν₅, ν₆, ν₈, and ν₉ was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are $\text{ν}{}_5{}^0\text{= 587.30 (27)}$ and $\text{ν}{}_6{}^0\text{= 528.36 (39)}\text{cm}{}^{\mathrm{?1}}$. Synthetic spectra indicate the band origins of ν₈ and ν₉ to be close to 977.8 and 439.0 cm^?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are $\text{ζ}{}_{58}{}^{\mathrm{a}}\text{= + 0.33 (5)}$, $\text{ζ}{}_{68}{}^{\mathrm{a}}\text{= + 0.714 (20)}$, $\text{ζ}{}_{59}{}^{\mathrm{a}}\text{= ? 0.774 (20)}$, and $\text{ζ}{}_{69}{}^{\mathrm{a}}\text{= ? 0.30 (2)}$. Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are $\text{M}{}_8{}^0\text{:±iM}{}_5{}^0\text{:±iM}{}_6{}^0\text{:M}{}_9{}^0\text{≈ +2:?9:+10:+0.5}$.     

Diode laser measurements of strengths,half-widths,and temperature dependence of half-widths for CO2 spectral lines near 4.2 μm

Absolute line strengths have been measured at room temperature for spectral lines in the R branch of the ν₃ band of ¹²C¹⁶O₂, ¹²C¹⁶O¹⁸O, and ¹²C¹⁶O¹⁷O and the (ν₂ + ν₃) ? ν₂ and (ν₁ + ν₃) ? ν₁ bands of ¹²C¹⁶O₂ in the region 2365–2393 cm^?1 using a tunable diode laser spectrometer; from these measurements band strengths have been computed. Self- and nitrogen-broadened half-widths have been measured for some ν₃ lines of ¹²C¹⁶O₂ and ¹²C¹⁶O¹⁷O, and nitrogen-broadened half-widths measured for some (ν₂ + ν₃) ? ν₂ band lines of ¹²C¹⁶O₂. From measurements made over a temperature range from 217 to 299 K we have obtained temperature coefficients n, for the N₂-broadened Lorentz half-width defined as $\text{b}{}_{\mathrm{L}}{}^0\text{(T) = b}{}_{\mathrm{L}}{}^0\text{(T}{}_0\text{)(}\text{T}\text{T}{}_0\text{)}{}^{\mathrm{?n}}$, for the ν₃ and (ν₂ + ν₃) ? ν₂ bands of ¹²C¹⁶O₂. They are 0.757 ± 0.008 and 0.789 ± 0.015, respectively.     

Acetylene fluorescence

Previously unobserved acetylene ${}^1\text{A}{}_{\mathrm{u}}\text{(}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}\text{) →}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ fluorescence occurs following 1933-Å ArF laser excitation of C₂H₂ or C₂H₄ and their deuterated analogs in solid Ne and Ar hosts at 4.2 K. Acetylene is a photolysis product of matrix-isolated ethylene. Ground-state vibrational levels as high as ν″₃ = 30 of the degenerate ν₃ bending vibration are observed for C₂D₂. Only ν₃ is appreciably active in the fluorescence. The negative ν₃ anharmonicity, previously observed in the gas phase, also occurs in Ne host. Consideration of rotational selection rules indicates that the Ne host strongly hinders free rotation about the low-moment-of-inertia $\text{a}\text{?}$ axis in the excited state.     

Selenium dioxide: Analysis of the 419-nm absorption system

The C absorption systems in the region 370–500 nm of the three isotopic species ⁷⁸Se¹⁶O₂, ⁸⁰Se¹⁶O₂, and ⁷⁸Se¹⁸O₂ have been comparatively studied in the vapor phase. The 0₀⁰ band is at 23840, 23840, and 23842 cm^?1, respectively. The vibrational structure consists of long progressions in the bending mode ν′₂(a₁) ～ 200 cm^?1, which are based on the origin band and on vibronic origins in which all three normal modes can be active. Most bands are severely overlapped, so that detailed rotational analyses are not possible. Band contour analysis of the 2₀²3₁⁰ band indicates that the transition is ${}^3\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$, which acquires intensity by both spin-orbit and spin-vibronic coupling mechanisms. The estimated bond length and angle in the triplet state are 1.69 Å and 100°, respectively, the latter representing a large decrease from the ground state value of 114°.     

Strengths and lorentz broadening coefficients for spectral lines in the ν3 and ν2 + ν4 bands of 12CH4 and 13CH4

Line strengths and self- and nitrogen-broadened half-widths were measured for spectral lines in the ν₃ and ν₂ + ν₄ bands of ¹²CH₄ and ¹³CH₄ from 2870–2883 cm^?1 using a tunable diode laser spectrometer. From measurements made over a temperature range from 215 to 297 K, on samples of ¹²CH₄ broadened with N₂, we deduced that the average temperature coefficients n, defined as $\text{b}{}_{\mathrm{<mtext>L</mtext>}}{}^0\text{(T) = b}{}_{\mathrm{<mtext>L</mtext>}}{}^0\text{(T}{}_0\text{)(}\text{T}\text{T}{}_0\text{)}{}^{\mathrm{?n}}$, of the Lorentz broadening coefficients for the ν₃ and ν₂ + ν₄ bands of ¹²CH₄ were 0.97 ± 0.03 and 0.89 ± 0.04, respectively. A smaller increase is observed in line half-width with increasing pressure for E-species lines, for both self- and nitrogen-broadening, than for other symmetry species lines over the range of pressures measured, 70 to 100 Torr.     

The high resolution infrared spectrum of the ν1 band of HOCl

The ν₁ bands of HO³⁵Cl and HO³⁷Cl have been recorded. Both the A- and B-type rotational transitions of these hybrid bands have been completely assigned, and spectroscopic constants have been obtained for both the ground and upper state. The ratio of the electric dipole moment derivatives $\text{(}\text{?μ}{}_{\mathrm{a}}\text{?Q}{}_1\text{)}\text{(}\text{?μ}{}_{\mathrm{b}}\text{?Q}{}_1$ has been found to be 0.985 ± 0.05 for ν₁.     

The two-photon excitation spectrum of fluorobenzene vapor

The two-photon excitation spectrum of fluorobenzene vapor has been recorded in the region of the $\text{A}\text{?}{}^1\text{B}{}_2\text{←}\text{X}\text{?}{}^1\text{A}{}_1$ transition. The spectrum shows considerable rovibronic structure with the bulk of the intensity lying in the subsystem induced by the ν₁₄(b₂) vibration. Two types of rovibronic contours, arising from ΔK_a = ±1 and from ΔK_a = 0, ±2 transitions, are identified. Major features in these contours are assigned by comparison with synthetic spectra, calculated using known upper and lower state rotational constants. The intensity distribution among the various bands in progressions of the totally symmetric vibrations is considerably different from that in the one-photon absorption spectrum, and the possible reasons for this are discussed.     

High-resolution infrared spectrum of the ν2 and ν8 bands of CH2D2

A high-resolution infrared spectrum of methane-d₂ has been measured in the C-D stretching band region (2025–2435 cm^?1). Rotational structures of the ν₂ and ν₈ bands have been assigned by use of the ASSIGN-diagram method, and the c-type Coriolis interaction between ν₂ and ν₈ has been analyzed. The band origins, ν₂ = 2203.22 ± 0.01 cm^?1 and ν₈ = 2234.70 ± 0.01 cm^?1, the rotational constants and the centrifugal distortion constants for the two bands, and the Coriolis coupling constant, $\text{∥;ξ}{}_{28}{}^{\mathrm{c}}\text{∥; = 0.182 ± 0.015}\text{cm}{}^{\mathrm{?1}}$, have been determined.     

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.