A study of the excited electronic states of 9-fluorenone

Some spectroscopic properties of the low-energy electronic states of 9-fluorenone have been examined. The spectra in paraffin matrices at 4.2°K show detailed vibrational spectra. Two fluorescence spectra are observed; a diffuse emission arises from 9-fluorenone crystals in the paraffin matrix, and a sharp emission is characteristic of the molecule. The sharp fluorescence is analyzed in terms of known a₁ vibrational fundamentals. The sharp absorption is a near mirror-image to the fluorescence, so Herzberg-Teller vibrations are not prominent. The polarization in the crystal spectrum allows this low-energy transition near 23 000 cm^?1 to be assigned ${}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1$. Because there is no vibronic perturbation in fluorescence, and certainly no out-of-plane modes, a $\text{π}{}^1\text{← n}$ transition seen at about 26 000 cm^?1 is tentatively assigned ${}^1\text{B}{}_1\text{←}{}^1\text{A}{}_1$. Another sharp absorption system is seen at 31 000 cm^?1 in the paraffin matrices at 4.2°K (linewidth 6 cm^?1) but no fluorescence was detected. The polarized crystal spectrum indicated the assignment of this system and another very strong system at 40 000 cm^?1 to be ${}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1$, while other systems at about 34 000 cm^?1 and 44 000 cm^?1 are ${}^1\text{A}{}_1\text{←}{}^1\text{A}{}_1$.The phosphorescence spectrum of pyrene-d₁₀ held in a single crystal of 9-fluorenone at 4.2°K has been recorded. No delayed fluorescence from the host crystal is observed at 4.2°K but is intense at 77°K. The energy difference between host and guest triplet levels is estimated to be about 900 cm^?1 allowing the lowest triplet state of 9-fluorenone to be placed at 17 800 cm^?1.     

The visible absorption spectrum of NO2: A three-mode nuclear dynamics investigation

The vibronic band origins of the visible absorption spectrum of NO₂ are calculated theoretically with the aid of a simple model Hamiltonian for the coupled electronic and vibrational motions. Including all three vibrational modes in the calculation and using ab initio values of the relevant parameters, we obtain satisfactory qualitative agreement with experiment. In particular, the observed high density and irregular intensity distribution of the band origins is reproduced correctly by the calculation. The present results confirm unambiguosly that the anomalous vibronic structure of the ${}^2\text{B}{}_2\text{←}{}^2\text{A}{}_1$ transition is caused by strong nonadiabatic interactions between the ²B₂ and ²A₁ electronic states of NO₂. They also show that simple deconvolution procedures, which are often used to deperturb irregular spectra, are not applicable to the ${}^2\text{B}{}_2\text{←}{}^2\text{A}{}_1$ transition of NO₂. To further explore the strength of the nonadiabatic effects in NO₂, we calculate the mixing of the different electronic species in the vibronic eigenstates and compare it to several relevant experimental quantities.     

The electronic states of nitroanilines

A correlation of spectroscopic data with all-valence-electron, $\text{CNDO}\text{s-CI}$ results has been performed for a number of mono- and disubstituted benzenes containing nitro and/or amino groups. The lowest energy transitions of p-nitroaniline are predicted to be 1¹B₁ ← 1¹A₁, 2¹A₁ ← 1¹A₁, and 2¹B₁ ← 1¹A₁, in the order of increasing energy. These three transitions are assigned to (i.e., are encompassed within) the lowest energy absorption band envelope of p-nitroaniline. The lowest energy predicted transition of o- and m-nitroanilines is 2A′ ← 1A′ and is supposed to correspond to the totality of the lowest energy absorption feature in both of these systems. The orbital excitation nature of these transitions is discussed.     

The 341 nm band system of pyridine-N-oxide. Analysis of the in-plane vibrational structure

The near-ultraviolet absorption of pyridine-N-oxide has been photographed at high resolution in the range 295–365 nm, and a weak, long-axis polarized subsystem of A-type bands has been identified in the spectrum for the first time. The presence of both A- and B-type bands in the system establishes conclusively that the transition is $\text{π}{}^1\text{← π [}{}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1\text{]}$.The complete set of a₁ and b₂ fundamental frequencies has been identified in the ground and excited states of the transition, using infrared and Raman measurements to supplement the data from the electronic analysis. Physical structure in the excited state has not been determined but appears qualitatively to involve a generalized increase in the dimensions of the ring, coupled with a decrease in the NO distance. The structure of the band system is very similar to that of isovalent aromatic molecules, including phenol and chlorobenzene.     

Fluorescence spectrum of chlorine dioxide induced by the 4765 Å argon-ion laser line

The fluorescence spectrum induced in ClO₂ by excitation with the 4765 Å argon-ion laser line has been studied under moderate resolution with the laser in single mode operation and under high resolution with the laser in multimode operation. The most intense features of the fluorescence have been assigned to excitation by the 23_{2, 22} ← 24_{2, 23} transition of the (0, 0, 0) ← (0, 0, 0) band of ³⁷ClO₂. Another set of features has been assigned to excitation by the 38_{0, 38} ← 37_{0, 37} transition of the (0, 0, 0) ← (0, 0, 0) band of ³⁷ClO₂.The vibrational structure and the ν₁ vibrational dependence of the rotational structure in the fluorescence have been least squares fitted giving a new set of vibrational constants and vibration-rotation interaction constants, $\text{α}{}_1{}^{\mathrm{B}}$ and $\text{α}{}_1{}^{\mathrm{C}}$.     

The A′(3Π2) state of ICl

Although $\text{A′(}{}^3\text{Π}{}_2\text{) ← X(}{}^1\text{Σ}{}^{\mathrm{+}}\text{)}$ is forbidden in near case c molecules the A′ ← X transition can be efficiently accomplished by the three-step sequence $\text{A′(}{}^3\text{Π}{}_2\text{) ← D′(2) ← A(}{}^3\text{Π}{}_1\text{) ← X(}{}^1\text{Σ}{}^{\mathrm{+}}\text{)}$. Transitions to a range of levels of A′, v_A′ = 2–38, have been recorded by this means, using J-selective polarization-labeling spectroscopy. Principal constants of the A′ state of I³⁵Cl are T_e = 12682.05, ω_e = 224.57, ω_eχ_e = 1.882, ω_ey_e = ?0.0107, B_e = 0.08653, and α_e = 0.000675 cm^?1. The A′ state is therefore similar in its physical characteristics to two other (relatively) deep states, $\text{A(}{}^3\text{Π}{}_1\text{)}$ and $\text{B(}{}^3\text{Π}{}_0\text{+)}$, of the 2431 configuration.     

Subject index for volume 88

The emission and excitation spectra of the aromatic thioketone xanthione have been measured in Shpolskii matrices at 15 K. Under these conditions a sharp and rich vibrational structure is observed in the lowest triplet and the first and second excited singlet states. The phosphorescence excitation spectrum places the origin of the T₁ ← S₀ transition at 15 143 cm^?1, while that of the $\text{S}{}_1\text{(n, π}{}^1\text{) ← S}{}_0$ absorption is tentatively assigned to the band at 16 093 cm^?1. The phosphorescence spectrum, which shows only a weak CS stretch vibrational band, is dominated by ring vibrations. In accordance with the previous analysis of ODMR measurements, it is suggested that T₁ and T₂ states are energetically very close, thereby resulting in a lowest triplet state of heavily mixed n, $\text{π}{}^1\text{-π}$, $\text{π}{}^1$ character. No mirror-image relationship is found between the relatively strong S₂ → S₀ fluorescence and the excitation spectrum of the $\text{S}{}_2\text{(π, π}{}^1\text{) ← S}{}_0$ transition. The latter is dominated by a long, pronounced 336-cm^?1 progression.     

The fluorescence excitation spectrum of s-tetrazine cooled in a supersonic free jet

The fluorescence excitation spectrum of the ${}^1\text{B}{}_{\mathrm{3u}}\text{(v′ = 0) ←}{}^1\text{A}{}_{\mathrm{g}}\text{(v″ = 0)}$ transition in s-tetrazine has been observed and measured. The sample was cooled to a rotational temperature of <1 K by expansion in a supersonic free jet. In this way the rotational structure arising from asymmetry split low J lines could be observed. The rotational A and B axes of the ²H₁¹²C₂¹⁴N₄ isotope were observed to interchange upon electronic excitation and a theory describing the effect of this interchange upon the optical selection rules has been developed. Analysis of the resolved rotational structure suggests that the geometry change upon electronic excitation is smaller than that deduced from previous analysis of the room temperature optical spectrum.     

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.     

Rotationally resolved infrared-ultraviolet double resonance spectroscopy in molecular D2CO and HDCO

Rotationally resolved infrared-ultraviolet double resonance (IRUVDR), consisting of sequentially excited rovibrational and rovibronic transitions sharing a common intermediate molecular level, is demonstrated. The technique employs pulsed CO₂ and tunable dye lasers and is applied to the molecules D₂CO and HDCO. For D₂CO, infrared pumping produces 100fold population enhancement in specific rotational sublevels of the v₄ = 1 level of the $\text{X}\text{?}{}^1\text{A}{}_1$ electronic ground state, followed by ultraviolet excitation in the 365-nm 4₁⁰ band of the $\text{A}\text{?}{}^1\text{A}{}_2\text{←}\text{X}\text{?}{}^1\text{A}{}_1$ electronic system. This ultraviolet excitation occurs at a specific set of dye laser frequencies, determined by the preceding rovibrational transition, and is detected by molecular fluorescence in the visible region. Similar effects observed in HDCO involve rovibrational pumping to either the v₆ = 1 or v₅ = 1 levels and give rise to enhanced rovibronic transitions in the 6₁⁰ and 5₁⁰ bands of the $\text{A}\text{?}\text{←}\text{X}\text{?}$ system, respectively. The resulting IRUVDR spectra enable detailed spectroscopic assignments to be made and are consistent with previous results from infrared and ultraviolet absorption, laser Stark, and infrared-radiofrequency double resonance spectroscopy. Collision-induced satellite structure, arising from rotational relaxation of the intermediate rovibrational level in the IRUVDR sequence, is also reported.     

Hyperfine spectra of bromine vapor near 633 nm

The hyperfine spectra of the (17-7)P(57) line of ⁷⁹Br₂ and the (12-4) P(129) line of ⁸¹Br₂, both of the electronic transition near 633 nm have been measured by the saturated absorption method. An analysis based on nuclear quadrupole and spin-rotation interactions is presented.     

Electric field-induced spectrum of carbon disulfide: Excited state dipole moment

The electric field-induced spectrum of carbon disulfide vapor has been observed in a number of vibronic bands in the 3300–3750 Å region of the $\text{B}{}_2\text{←}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ electronic system. A detailed analysis of the Σ0^g+2 band at 29 241.8 cm^?1 has yielded the electric dipole moment of the bent excited state of the transition as 0.7 ± 0.1 D.Consideration of the lineshapes of the EFS lines in this band gives a confirmation of the value of A′ near 4.3 cm^?1. The ratio of induced absorption intensities perpendicular and parallel to the applied field in various bands correlates with the band-type assignments of Klemens.     

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.     

Ultraviolet absorption spectra of Zn2 and Cd2 in solid argon and krypton at 10 K

Zinc and cadmium atoms have been condensed with argon and krypton at 10 K. The most intense absorption is due to the ${}^1\text{P}{}_1\text{←}{}^1\text{S}{}_0$ atomic transition, and a weak band is due to the ${}^3\text{P}{}_1\text{←}{}^1\text{S}{}_0$ atomic absorption. Structured absorptions at 252 and 254 nm in solid argon and krypton with vibrational spacings of 140-120 cm^?1 are due to the ${}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{←}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transition of Zn₂. Similar 273 and 277 nm absorptions with 110-90 cm^?1 vibrational spacings are due to Cd₂ in solid argon and krypton, respectively.     

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.     

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.     

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.     

Near-uv spectra with fully resolved rotational structure of naphthalene and perdeuterated naphthalene

The combination of a single-frequency, tunable uv source with a well-collimated supersonic molecular beam and sensitive fluorescence detection has been used to obtain spectra with rovibronic resolution for some large organic molecules. The results of analysis of the 0₀⁰ and $\text{8}$₀¹ vibronic bands of the ${}^1\text{B}{}_{\mathrm{3u}}\text{←}{}^1\text{A}{}_{\mathrm{g}}$ electronic transition for naphthalene and naphthalene-d_g are presented. The obtained spectra are assigned using a rigid asymmetric rotor Hamiltonian and the structure in both the ground and electronically excited states is determined. The rotational temperature of the molecules cooled in the beam has been determined. The influence of the nuclear spin statistics on the line intensities is observed and discussed.     

Infrared diode laser spectroscopy of the NS radical

The v = 1 ← 0 vibration-rotation bands of the NS radical in the $\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ electronic states were observed by using a tunable diode laser. From the least-squares analysis the band origins were determined to be 1204.2755(12) and 1204.0892(19) cm^?1, respectively, for $\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$. The rotational and centrifugal distortion constants and the internuclear distance in the X²Π electronic state were obtained as follows: B_e = 0.775549(10) cm^?1, D_e = 0.00000129(33) cm^?1, and $\text{r}{}_{\mathrm{e}}\text{= 1.49403(4)}\text{A}\text{?}$, with three standard deviations indicated in parentheses.     

S1-S0 fluorescence after narrow band excitation of glyoxal: Single rotational level fluorescence and a technique for deconvolution of Doppler congested absorptions

Individual rovibronic transitions are isolated at high resolution from a crowded absorption feature with a fluorescence excitation technique which is based on detection of fluorescence from one and only one rovibronic level. The method is illustrated by resolving four rovibronic transitions from the single rotational line-like feature in the 0, 0 band of the ${}^1\text{A}{}_{\mathrm{u}}\text{←}{}^1\text{A}{}_{\mathrm{g}}$ (S₁ ← S₀) absorption of glyoxal vapor. The rotational structure of the 5₁⁰ fluorescence band is studied as a function of tuning a narrow-band laser line (linewidth < 10^?4 cm^?1) to various positions in and near this absorption feature. The fluorescence structure proves an extremely sensitive tool for detecting small absorptions, with emission from 12 rovibronic levels being identified. One of the spectra so obtained is a close approximation of true single rotational level fluorescence.