The characterization of the complete set of bound vibronic states of HNO in its excited Ã1A″ electronic state

Laser-induced fluorescence excitation spectra of the HNO $\text{A}\text{?}{}^1\text{A″-}\text{X}\text{?}{}^1\text{A′}$ band system have been recorded with high sensitivity. This has enabled detection of the Franck-Condon unfavored vibronic bands (002)-(000) and (003)-(000), thereby completing the set of fully bound vibronic levels in the $\text{A}\text{?}$ state. Extensions have also been made to other bands. A strong Coriolis resonance between the K_a¹ = 8 levels of the excited (010) vibronic state and the K_a¹ = 9 levels of the (001) state leads to rotational perturbations of up to 9 cm^?1. The (100-000) band includes weak axis-tilting branches. It is concluded from the vibrational energy level spacings that vibronic interaction makes an important contribution to the energies of the higher bending levels, consistent with the correlation of the $\text{A}\text{?}{}^1\text{A″}$ state with a component of a ¹Δ state for linear HNO.     

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.     

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°.     

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.     

Laser-induced fluorescence spectroscopy of the E band of the Ã-X̃ transition of SO2 cooled rotationally in a supersonic jet

The rotationally resolved, laser-induced fluorescence spectrum of the E band of the $\text{A}\text{?}{}^1\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ transition of SO₂ seeded in a supersonic jet was observed, and each rotational line was assigned on the basis of the ground state combination differences and the relative intensity data as a function of the rotational temperature. It was demonstrated that the line congestion was reduced significantly in the spectrum of the jet, and some of the lines, e.g., ^rR₀(0), were assigned unambiguously. This makes it possible to determine the vibronic band origin with an error of less than 0.2 cm^?1.     

Doppler-limited dye laser excitation spectroscopy of the DSO radical

The $\text{A}\text{?}{}^2\text{A′(003) ←}\text{X}\text{?}{}^2\text{A″(000)}$ vibronic transition (16 370 to 16 425 cm^?1) of the DSO radical in studied by Doppler-limited dye laser excitation spectroscopy. DSO is produced in a flow system by reacting the products of a microwave discharge in O₂ with D₂S. About 637 observed lines are assigned to 987 transitions of the 19 subbands: K′_a ← K″_a = 6 ← 5, 5 ← 4, 4 ← 3, 3 ← 2, 2 ← 1, 1 ← 0, 0 ← 1, 1 ← 2, 2 ← 3, 3 ← 4, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 4 ← 4, 3 ← 1, 2 ← 0, 0 ← 2, and 1 ← 3. They are analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation constants for both the ground and the excited electronic states. The band origin obtained is 16 413.874 (2.5σ = 0.002) cm^?1. The rotational constants determined are combined with the previous result on HSO (M. Kakimoto et al., J. Mol. Spectrosc.80, 334–350 (1980)) to calculate the structural parameters for this radical in both the states: $\text{r(}\text{SO}\text{) = 1.494(5)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.389(5)}\text{A}\text{?}$, and ∠HSO = 106.6(5)° for the $\text{X}\text{?}{}^2\text{A″}$ state, and $\text{r(}\text{SO}\text{) = 1.661(10)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.342(8)}\text{A}\text{?}$, and ∠HSO = 95.7(21)° for the $\text{A}\text{?}{}^2\text{A′(003)}$ state, where values in parentheses denote 2.5σ.     

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.     

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°.     

Two-photon excitation of the C̃1B2 state of sulfur dioxide

The two-photon excitation (TPE) spectrum of sulfur dioxide is reported in the region of the $\text{C}\text{?}{}^1\text{B}{}_2\text{←}\text{X}\text{?}{}^1\text{A}{}_1\text{[2b}{}_1\text{(π}{}^1\text{) ← 1a}{}_2\text{(π)]}$ transition. The spectrum shows considerable rovibronic structure; the band contours are identified as arising from ΔK_?1 = ± 1 transitions and rotational features are assigned by comparison with synthetic spectra generated from known rotational constants. The vibronic structure observed in TPE is quite similar to that observed in the one-photon spectrum: no zero-rank tensor transitions to levels with odd v₃ are identified, though they are allowed in the presence of vibronic coupling. The vibronic intensity distribution in the TPE spectrum below the dissociation limit is similar to that in one-photon absorption. However, near the dissociation threshold (5.63–5.67 eV), marked intensity redistribution occurs, from which it is concluded that the lowest energy photo-dissociation process proceeds through asymmetric stretching of the SO bonds.     

The 3B1-1A1 band system of sulfur dioxide: Rotational analysis of the (010), (100), and (110) bands

The (010)-(000) band of the ${}^3\text{B}{}_1\text{←}{}^1\text{A}{}_1$ system of sulfur dioxide has been rotationally analyzed and constants for the magnetic interactions in the (010) vibrational level determined. Partial rotational analyses are given for the rotationally perturbed (100)-(000) and (110)-(000) bands of the system. The extensive perturbations in this band system are provisionally attributed to: (i) vibronic interaction with a ³A₂ state, visible (a) as a large negative anharmonicity in higher bands of the ³B₁ system, and (b) as a ΔK = 0 resonance perturbation in low-lying vibrational levels of the ³B₁ state; and (ii) a K, K ± 1N-dependent perturbation possibly due to rotational-electronic coupling with a ³B₂ state, though evidence on this point is incomplete. Evidence bearing on these conclusions is discussed.     

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 uv spectrum of 18OD

The combined high-resolution ultraviolet (uv) absorption spectrum of ¹⁶OD and ¹⁸OD was obtained. State selective measurements of the transitions from the electronic ground state to the first excited electronic state, $\text{A}\text{?}{}^2\text{Σ}{}^{\mathrm{+}}\text{←}\text{X}\text{?}{}^2\text{Π}$, in the 0-0 vibronic band were performed by means of a narrow bandwidth dye laser system. Evaluation of these transition frequencies in wave-numbers yielded molecular constants as well as rotational term values for each of the isotopic species. A computer program based on a linearized least-squares procedure was used to determine the molecular constants and term values. The term value formulas which were employed for this purpose, take into account the Λ splitting and the centrifugal distortion of the diatomic species. The transitions, recalculated from the semiempirically determined term values agree with the measured absorption lines to better than 0.1 cm^?1. The following molecular constants are reported: B, D, H, the rotational constants of the ²Π and ²Σ⁺ states; O₀, P₀, Q₀, the constants of the Λ splitting of the ²Π state; A and A₁; the constants of the spin-orbit coupling of the ²Π state; and γ₀, the constant of the p doubling of the ²Σ⁺ state. Futhermore, term values up to J″ and J′ of 25.5 and the corresponding uv transitions are given.     

Equilibrium structure and force field of nitrosyl chloride

The a-type rotational spectra of ¹⁶O¹⁵N³⁵Cl in the (100) excited vibrational state ($\text{ν}{}_1\text{? 1770}\text{cm}{}^{\mathrm{?1}}$) and of ¹⁸O¹⁵N³⁵Cl and ¹⁸O¹⁴N³⁷Cl in the ground state were observed. The equilibrium structure of nitrosyl chloride was calculated from the values of the equilibrium rotational constants B_e and C_e of the two isotopic species ¹⁶O¹⁴N³⁵Cl and ¹⁶O¹⁵N³⁵Cl. The ground-state rotational constants of seven isotopic species of nitrosyl chloride were used to calculate Watson's r_m structure, which was found to be in satisfactory agreement with the r_e structure. The quadratic and cubic force fields of nitrosyl chloride were simultaneously refined by optimizing the least-squares fit to a set of 48 experimental data which includes the sextic centrifugal distortion constants, with one quadratic and three cubic terms of the potential energy function constrained to the values computed by SCF/ab initio methods. All remaining quadratic and cubic SCF force constants were found to be in reasonably close agreement with the empirically determined constants.     

High resolution vibration-rotation spectra of carbon suboxide: Molecular constants for the ground state and 2ν70

The infrared spectrum of C₃O₂ was recorded with the vacuum Fourier transform interferometer of Laboratoire Aimé Cotton at a resolution of 0.005 cm^?1. The ground state molecular constants were calculated from lower state combination relations in a simultaneous analysis of six ground state transitions situated in the region 3000 to 5000 cm^?1. Through the analysis of a difference band we established that $\text{2ν}{}_7{}^0$ is 60.7022 ± 0.0005 cm^?1 above the ground vibrational state. Accurate molecular constants were also determined for this vibrational level.     

Rotational analysis of the 8000–9000 Å bands of nitrogen dioxide

The rotational structure of bands of NO₂ vapor in the region 8300–9000 Å has been partially analyzed and the absorption assigned to the (000)-(000) and (000)-(010) vibronic bands of the $\text{A}\text{?}{}^2\text{B}{}_2\text{←}\text{X}\text{?}{}^2\text{A}{}_1$ electronic transition. Irregular weak perturbations in the N-structure of the upper-state manifold are accompanied by larger resonance-type crossings in the K-structure. The larger perturbation is attributed to vibronic coupling between the à state and excited vibrational levels of the ground state, characterized by a low density of ground state levels and a large vibronic coupling matrix element between the à and X? states. The reconstituted, deperturbed bands have blue-degraded N-structure and strongly red-degraded K-structure, indicating that the bond angle decreases sharply in the excited state. The physical structure of the ²B₂ state is uncertain but some suggestions are made. The electronic energy of the ²B₂ state is T₀ = 11 962.9 cm^?1.     

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°.     

Vibrational spectra and force constants of symmetric tops: High resolution spectra of monoisotopic H3SiCl in the 2200-cm−1 region and rovibrational analysis of the ν1 and ν4 fundamentals

The gas phase infrared spectra of monoisotopic H₃Si³⁵Cl and H₃Si³⁷Cl have been studied in the $\text{ν}{}_1\text{ν}{}_4$ region near 2200 cm^?1 with a resolution of 0.012 and 0.04 cm^?1, respectively, and rotational fine structure for ΔJ = ±1 branches has been resolved. In addition, some information on ν₃ + ν₄ of H₃Si³⁵Cl near 2750 cm^?1 has been obtained. ν₁ and ν₄ are weakly coupled by Coriolis x, y resonance, $\text{B}\text{Ω}{}_{14}\text{ζ}{}_{14}\text{～ 2 × 10}{}^{\mathrm{?3}}\text{cm}{}^{\mathrm{?1}}$, only the upper states K′ = 2, l = 0 and K′ = 1, l = ?1 being substantially affected. Local perturbation due to rotational l(±1, ±1)-type resonance with ν₃ + ν₅⁺¹ + ν₆⁺¹ and ν₃ + ν₅⁺¹ + ν₆^?1 is revealed in the ΔK = +1 and ?1 branches, respectively. From a fit of the experimental line positions, standard deviations of 1.4 and 3.8 × 10^?3 cm^?1, respectively, to a model with five interacting levels conventional excited state parameters and interaction constants have been obtained. In $\text{H}{}_3\text{Si}{}^{35}\text{Cl}\text{H}{}_3\text{Si}{}^{37}\text{Cl}$ the fundamentals are ν₁, $\text{2201.94380(15)}\text{2201.9345(7)}$ and ν₄, $\text{2209.63862(8)}\text{2209.6254(2)}\text{cm}{}^{\mathrm{?1}}$, respectively. Q branches of the “hot” band (ν₃ + ν₄) ? ν₃ and of ν₄ of the ²⁹Si and ³⁰Si species have been detected.     

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.     

Electronic spectrum of 1,5-naphthyridine: Crystal spectra

Polarized spectra (4 K) of the following systems are recorded in the region 26 000 – 29 000 cm^?1 ($\text{π}{}^1\text{← n}$ transition): 1,5-naphthyridine-d₀ in durene, p-xylene, neat crystal and naphthalene; 1,5-naphthyridine-d₆ in durene and in naphthalene. The spectra in naphthalene differ radically from the others, which resemble the vapor spectrum in being built principally upon two main origins interpreted as the true origin 0 and a vibronic origin (6a_u)₀¹ near 0 + 183 cm^?1 (0 + 163 cm^?1, -d₆). The favored interpretation of the naphthalene spectrum, which is polarized in the molecular plane, invokes an origin (L-polarized), but (6a_u)₀¹ is missing, and there are then three further vibronic origins, each with distinctive polarization at 0 + 309, 0 + 362, 0 + 516 cm^?1 (-d₀), 0 + 312, 0 + 384, 0 + 492 cm^?1 (-d₆). The changed appearance of the spectrum in naphthalene is attributed to a diminution, because of an increased spacing between the interacting states, of the strong vibronic coupling which is considered to exist between the n, $\text{π}{}^1$ state and two higher π, $\text{π}{}^1$ states.     

Analysis of the perturbed NO22B2 ← 2A1 system in the 591.4- to 592.9-nm region based on sub-Doppler laser spectroscopy

Sub-Doppler excitation spectra of NO₂, covering four vibronic bands within the spectral range from 16 861 to 16 903 cm^?1, were measured with a resolution of down to 10 MHz in a collimated supersonic molecular beam. Unambiguous assignment of all prominent lines in the 42-cm^?1-wide interval of the ${}^2\text{B}{}_2\text{←}{}^2\text{A}{}_1$ excitation spectrum was achieved by recording for each excitation line at least four vibrational bands of the corresponding fluorescence spectrum with completely resolved rotational lines. From least-squares fits to the line positions in the excitation spectra the rotational, fine, and hyperfine structure of the ²B₂ state was analyzed. A perturbation analysis, based on information from both types of spectra, confirms earlier models of vibronic coupling with high-lying vibrational levels of the ²A₁ ground state and gives evidence for spin-orbit coupling. Possible models are discussed which may explain the observed perturbations.