Photodissociation of Cl2SO at 248 and 193 nm in a molecular beam

A pulse molecular beam of Cl₂SO was photodissociated at 248 and 193 nm. The time-of-flight distributions were observed for the photofragments, Cl, ClSO and SO. The primary processes are Cl + ClSO (I), 2Cl + SO (II) and Cl₂ + SO (III). At 193 nm the measured translational energy distributions imply a vibrationally excited ClSO fragment in process (I), and a simultaneous dissociation in process (II). The relative quantum yield is φ_I < φ_II. At 248 nm a radical process (I) is dominant compared to a molecular process (III).     

Infrared absorption of CH3SO2 detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a 6.4 m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH3SO2 radical, produced upon irradiation of a flowing gaseous mixture of CH3I and SO2 in CO2 at 248 nm. Two transient bands with origins at 1280 and 1076 cm(-1) were observed and are assigned to the SO2-antisymmetric and SO2-symmetric stretching modes of CH3SO2, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH3SO2 and CH3OSO. Based on predicted rotational parameters, the simulated absorption band of the SO2-antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm(-1) observed at a later period is tentatively attributed to CH3SO2I. The reaction kinetics of CH3 + SO2 --> CH3SO2 and CH3SO2 + I --> CH3SO2I based on the rise and decay of absorption bands of CH3SO2 and CH3SO2I agree satisfactorily with previous reports.     

Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy

A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.     

Transient infrared spectra of CH3SOO and CH3SO observed with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to monitor time-resolved infrared absorption of transient species produced upon irradiation at 248 nm of a flowing mixture of CH(3)SSCH(3) and O(2) at 260 K. Two transient bands observed with origins at 1397±1 and 1110±3 cm(-1) are tentatively assigned to the antisymmetric CH(3)-deformation and O-O stretching modes of syn-CH(3)SOO, respectively; the observed band contour indicates that the less stable anti-CH(3)SOO conformer likely contributes to these absorption bands. A band with an origin at 1071±1 cm(-1), observed at a slightly later period, is assigned to the S=O stretching mode of CH(3)SO, likely produced via secondary reactions of CH(3)SOO. These bands fit satisfactorily with vibrational wavenumbers and rotational contours simulated based on rotational parameters of syn-CH(3)SOO, anti-CH(3)SOO, and CH(3)SO predicted with density-functional theories B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ. Two additional bands near 1170 and 1120 cm(-1) observed at a later period are tentatively assigned to CH(3)S(O)OSCH(3) and CH(3)S(O)S(O)CH(3), respectively; both species are likely produced from self-reaction of CH(3)SOO. The production of SO(2) via secondary reactions was also observed and possible reaction mechanism is discussed.     

Infrared absorption of C6H5SO2 detected with time-resolved Fourier-transform spectroscopy

C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm-1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.     

Infrared absorption of CH3OSO detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to detect temporally resolved infrared absorption spectra of CH(3)OSO produced upon irradiation of a flowing gaseous mixture of CH(3)OS(O)Cl in N(2) or CO(2) at 248 nm. Two intense transient features with origins near 1152 and 994 cm(-1) are assigned to syn-CH(3)OSO; the former is attributed to overlapping bands at 1154 ± 3 and 1151 ± 3 cm(-1), assigned to the S=O stretching mixed with CH(3) rocking (ν(8)) and the S=O stretching mixed with CH(3) wagging (ν(9)) modes, respectively, and the latter to the C-O stretching (ν(10)) mode at 994 ± 6 cm(-1). Two weak bands at 2991 ± 6 and 2956 ± 3 cm(-1) are assigned as the CH(3) antisymmetric stretching (ν(2)) and symmetric stretching (ν(3)) modes, respectively. Observed vibrational transition wavenumbers agree satisfactorily with those predicted with quantum-chemical calculations at level B3P86∕aug-cc-pVTZ. Based on rotational parameters predicted at that level, the simulated rotational contours of these bands agree satisfactorily with experimental results. The simulation indicates that the S=O stretching mode of anti-CH(3)OSO near 1164 cm(-1) likely makes a small contribution to the observed band near 1152 cm(-1). A simple kinetic model of self-reaction is employed to account for the decay of CH(3)OSO and yields a second-order rate coefficient k=(4 ± 2)×10(-10) cm(3)molecule(-1)s(-1).     

Cl2O photochemistry: ultraviolet/vis absorption spectrum temperature dependence and O(3P) quantum yield at 193 and 248 nm

The photochemistry of Cl(2)O (dichlorine monoxide) was studied using measurements of its UV/vis absorption spectrum temperature dependence and the O((3)P) atom quantum yield, Φ(Cl(2)O)(O)(λ), in its photolysis at 193 and 248 nm. The Cl(2)O UV/vis absorption spectrum was measured over the temperature range 201-296 K between 200 and 500 nm using diode array spectroscopy. Cl(2)O absorption cross sections, σ(Cl(2)O)(λ,T), at temperatures <296 K were determined relative to its well established room temperature values. A wavelength and temperature dependent parameterization of the Cl(2)O spectrum using the sum of six Gaussian functions, which empirically represent transitions from the ground (1)A(1) electronic state to excited states, is presented. The Gaussian functions are found to correlate well with published theoretically calculated vertical excitation energies. O((3)P) quantum yields in the photolysis of Cl(2)O at 193 and 248 nm were measured using pulsed laser photolysis combined with atomic resonance fluorescence detection of O((3)P) atoms. O((3)P) quantum yields were measured to be 0.85 ± 0.15 for 193 nm photolysis at 296 K and 0.20 ± 0.03 at 248 nm, which was also found to be independent of temperature (220-352 K) and pressure (17 and 28 Torr, N(2)). The quoted uncertainties are at the 2σ (95% confidence) level and include estimated systematic errors. ClO radical temporal profiles obtained following the photolysis of Cl(2)O at 248 nm, as reported previously in Feierabend et al. [J. Phys. Chem. A 114, 12052, (2010)], were interpreted to establish a <5% upper-limit for the O + Cl(2) photodissociation channel, which indicates that O((3)P) is primarily formed in the three-body, O + 2Cl, photodissociation channel at 248 nm. The analysis also indirectly provided a Cl atom quantum yield of 1.2 ± 0.1 at 248 nm. The results from this work are compared with previous studies where possible.     

Infrared absorption of gaseous benzoylperoxy radical C6H5C(O)OO recorded with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of benzoyl radical, C(6)H(5)CO, with O(2). C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm, or from photolysis of a mixture of benzaldehyde, C(6)H(5)CHO, and Cl(2) at 355 nm. Two intense bands near 1830 and 1226 cm(-1) are assigned to the C=O stretching (ν(6)) and the C-C stretching mixed with C-H deformation (ν(13)) modes, and two weaker bands near 1187 and 1108 cm(-1) are assigned to the ν(14) (C-H deformation) and ν(16) (O-O stretching /C-H deformation) modes of C(6)H(5)C(O)OO, the benzoylperoxy radical. These observed vibrational wave numbers and relative infrared intensities agree with those reported for syn-C(6)H(5)C(O)OO isolated in solid Ar and values predicted for syn-C(6)H(5)C(O)OO with the B3LYP/cc-pVTZ method. The simulated rotational contours of the two intense bands based on rotational parameters predicted with the B3LYP∕cc-pVTZ method fit satisfactorily with experimental results.     

Visible absorption spectrum of the CH3CO radical

The visible absorption spectrum of the acetyl radical, CH(3)CO, was measured between 490 and 660 nm at 298 K using cavity ring-down spectroscopy. Gas-phase CH(3)CO radicals were produced using several methods including: (1) 248 nm pulsed laser photolysis of acetone (CH(3)C(O)CH(3)), methyl ethyl ketone (MEK, CH(3)C(O)CH(2)CH(3)), and biacetyl (CH(3)C(O)C(O)CH(3)), (2) Cl + CH(3)C(O)H --> CH(3)C(O) + HCl with Cl atoms produced via pulsed laser photolysis or in a discharge flow tube, and (3) OH + CH(3)C(O)H --> CH(3)CO + H(2)O with two different pulsed laser photolysis sources of OH radicals. The CH(3)CO absorption spectrum was assigned on the basis of the consistency of the spectra obtained from the different CH(3)CO sources and agreement of the measured rate coefficients for the reaction of the absorbing species with O(2) and O(3) with literature values for the CH(3)CO + O(2) + M and CH(3)CO + O(3) reactions. The CH(3)CO absorption spectrum between 490 and 660 nm has a broad peak centered near 535 nm and shows no discernible structure. The absorption cross section of CH(3)CO at 532 nm was measured to be (1.1 +/- 0.2) x 10(-19) cm(2) molecule(-1) (base e).     

Infrared absorption of gaseous CH3OO detected with a step-scan Fourier-transform spectrometer

CH(3)OO radicals were produced upon irradiation of a flowing mixture of CH(3)I and O(2) with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved IR absorption spectra of reaction intermediates. Transient absorption bands with origins at 3033, 2954, 1453, 1408, 1183, 1117, 3020, and 1441 cm(-1) are assigned to nu(1)-nu(6), nu(9), and nu(10) modes of CH(3)OO, respectively, close to wavenumbers reported for CH(3)OO isolated in solid Ar. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predicted the geometry and the vibrational wavenumbers of CH(3)OO; the vibrational wavenumbers and relative IR intensities of CH(3)OO agree satisfactorily with these observed features. The rotational contours of IR spectra of CH(3)OO, simulated based on ratios of predicted rotational parameters for the upper and lower states and on experimental rotational parameters of the ground state, agree satisfactorily with experimental results; the mixing ratios of a-, b-, and c-types of rotational structures were evaluated based on the direction of dipole derivatives predicted quantum chemically. A feature at 995 cm(-1), ascribed to CH(3)OOI from a secondary reaction of CH(3)OO with I, was also observed.     

Determination of the rate constants for the NCO(X2Pi) + Cl(2P) and Cl(2P) + ClNCO(X1A') reactions at 293 and 345 K

The rate constant for the reaction of the isocyanato radical, NCO(X2Pi) with chlorine atoms, Cl(2P), has been measured at 293 +/- 2 and 345 +/- 3 K to be (6.9 +/- 3.8) x 10(-11) and (4.0 +/- 2.2) x 10(-11) cm3 molecules(-1) s,(-1) respectively, where the uncertainties include both random and systematic errors. The measurements were carried out at pressures of 1.3-6.2 Torr with either Ar or CF4 as the bath gas and were independent of both pressure and nature of the third body. Equal concentrations of NCO and Cl atoms were created by 248 nm photolysis of ClNCO. The reaction was monitored by following the temporal dependence of NCO(X2Pi) using time-resolved infrared absorption spectroscopy on rotational transitions of the NCO(10(1)1) <-- (00(1)0) combination band. The reaction rate constant was determined by using a simple chemical model and minimizing the sum of the residuals between the experimental and computer generated temporal NCO concentration profiles. The reaction Cl + ClNCO --> Cl2 + NCO was found to contribute to the observed NCO. The rate constant for this reaction was found to be (2.4 +/- 1.6) x 10(-13) and (1.9 +/- 1.2) x 10(-13) cm3 molecules(-1) s,(-1) at 293 and 345 K, respectively, where the uncertainties include both random and systematic error.     

Measurement of absolute absorption cross sections for nitrous acid (HONO) in the near-infrared region by the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique coupled to laser photolysis

Absolute absorption cross sections for selected lines of the OH stretch overtone 2ν(1) of the cis-isomer of nitrous acid HONO have been measured in the range 6623.6-6645.6 cm(-1) using the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique. HONO has been generated by two different, complementary methods: in the first method, HONO has been produced by pulsed photolysis of H(2)O(2)/NO mixture at 248 nm, and in the second method HONO has been produced in a continuous manner by flowing humidified N(2) over 5.2 M HCl and 0.5 M NaNO(2) solutions. Laser photolysis synchronized with the cw-CRDS technique has been used to measure the absorption spectrum of HONO produced in the first method, and a simple cw-CRDS technique has been used in the second method. The first method, very time-consuming, allows for an absolute calibration of the absorption spectrum by comparison with the well-known HO(2) absorption cross section, while the second method is much faster and leads to a better signal-to-noise ratio. The strongest line in this wavelength range has been found at 6642.51 cm(-1) with σ = (5.8 ± 2.2) × 10(-21) cm(2).     

Infrared absorption of gaseous benzoyl radical C6H5CO recorded with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C(6)H(5)CO. C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm or in reactions of phenyl radical (C(6)H(5)) with CO; C(6)H(5) was produced on photolysis of C(6)H(5)Br at 248 nm. One intense band at 1838 ± 1 cm(-1), one weak band at 1131 ± 3 cm(-1), and two extremely weak bands at 1438 ± 5 and 1590 ± 10 cm(-1) are assigned to the C═O stretching (ν(6)), the C-C stretching mixed with C-H deformation (ν(15)), the out-of-phase C(1)C(2)C(3)/C(5)C(6)C(1) symmetric stretching (ν(10)), and the in-phase C(1)C(2)C(3)/C(4)C(5)C(6) antisymmetric stretching (ν(7)) modes of C(6)H(5)CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C(6)H(5)CO isolated in solid Ar and with values predicted for C(6)H(5)CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm(-1) simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C(6)H(5)C(O)Br, and C(6)H(5)C(O)C(6)H(5) were identified in the C(6)H(5)Br/CO/N(2) experiments; the kinetics involving C(6)H(5)CO and C(6)H(5)C(O)Br are discussed.     

On the spin-orbit splitting of CuCl2 in its 2 Pi g ground state

The spin-orbit splitting of CuCl(2) in its ground X(2)Pi(g) state remains an unknown or, at best, poorly defined quantity. The electronic spectrum of CuCl(2) has been studied by Fourier transform resolved, laser-induced fluorescence between 602 and 587 nm, in an attempt to identify transitions to the upper spin component of the ground state. In order to provide a well-defined excitation process, the sample was cooled to rotational temperatures of about 10 K in a free-jet expansion. Observations from just two rotationally perturbed levels in the upper electronic state, one for (63)Cu(35)Cl(2) and the other for (65)Cu(35)Cl(37)Cl, have revealed an additional feature about 482 cm(-1) above the (2)Pi(3/2) state. The effective rotational constants associated with these levels (0.066 20 cm(-1) for (63)Cu(35)Cl(2)) are significantly larger than those for the ground (2)Pi(3/2) state (0.058 13 cm(-1)). Analysis of this feature as the (2)Pi(1/2) component leads to a value of -482.9 cm(-1) for the spin-orbit coupling constant A and of -0.0846 cm(-1) for the lambda-doubling parameter (p+2q) for (63)Cu(35)Cl(2). Several other previously unobserved levels are also identified within 2000 cm(-1) of the ground state. Many of these also have anomalously large rotational constants.     

Studies on the effects of metal ions and counter anions on the aggregate behaviors of meso-tetrakis(p-sulfonatophenyl)porphyrin by absorption and fluorescence spectroscopy

The aggregation behaviors of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) in the function of metal ions and their counter anions (Cl(-), SO(4)(2-), and NO(3)(-)) were investigated by absorption, fluorescence spectroscopy and resonance scattering spectrum. It was shown that the TPPS J-aggregates could be effectively promoted by metal ions under lower ionic strength. Moreover, the prominent effects of counter ions (Cl(-), SO(4)(2-), and NO(3)(-)) on TPPS J- and/or H-aggregate formation at higher ionic strength were observed. These results suggested that the counter anions play a significant role in the formation of TPPS J- and/or H-aggregates and their conversion each other. Very interestingly, the absorption spectrum of metal ions investigated except for Co(2+) leaves a WINDOW from ca. 450 to 550nm centered at 490nm in which the absorption of Cu(2+) or Ni(2+) ions per se was very weak. The spectrum window might be really significant in avoiding possible spectrum interferences when porphyrins are chosen as spectrometric reagents for the determination of metal ions based on J-aggregation.     

The ultraviolet spectrum of the CoCl2 radical, studied at vibrational and rotational resolution

The laser excitation spectrum of the 327 nm band system of CoCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. The spectrum is congested and suffers extensive perturbations. A progression in the excited state symmetric stretching vibration has been identified. The decrease in the symmetric stretching vibrational wave number on excitation is considerable [nu1 '=195.7(12), nu1 (")=358.1(17) cm(-1)]. Despite widespread perturbations in the rotational structure of these vibronic bands, they can be confidently assigned to a parallel Omega=72-72 transition, consistent with an inverted 4Deltag ground electronic state. The rotational constant for Co35Cl2 in the ground state is determined to be 0.056 65(11) cm(-1), which corresponds to a value for the zero-point averaged Co-Cl bond length r0 of 2.062 8(40) A. The perturbations are found to be strongly isotopomer dependent.     

Ab initio studies on vibrational spectra of XSO_2NCO (X=F,Cl):harmonic force fields and frequency assignments

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Unraveling the A(1)B1 <-- X(1)A1 spectrum of CCl2: The Renner-Teller effect, barrier to linearity, and vibrational analysis using an effective polyad Hamiltonian

We report studies aimed at unraveling the complicated structure of the CCl 2 A (1)B 1 <-- X (1)A 1 system. We have remeasured the fluorescence excitation spectrum from approximately 17,500 to 24,000 cm (-1) and report the term energies and A rotational constants of many new bands for both major isotopologues (C (35)Cl 2, C (35)Cl (37)Cl). We fit the observed term energies to a polyad effective Hamiltonian model and demonstrate that a single resonance term accounts for much of the observed mixing, which begins approximately 1300 cm (-1) above the vibrationless level of the A (1)B 1 state. The derived A (1)B 1 vibrational parameters are in excellent agreement with ab initio predictions, and the mixing coefficients deduced from the polyad model fit are in close agreement with those derived from direct fits of single vibronic level (SVL) emission intensities. The approach to linearity and thus the Renner-Teller (RT) intersection is probed through the energy dependence of the A rotational constant and fluorescence lifetime measurements, which indicate a barrier height above the vibrationless level of the X (1)A 1 state of approximately 23,000-23,500 cm (-1), in excellent agreement with ab initio theory.     

Br2 molecular elimination in 248 nm photolysis of CHBr2Cl by using cavity ring-down absorption spectroscopy

Elimination of molecular bromine is probed in the B (3)Pi(ou) (+)<--X (1)Sigma(g) (+) transition following photodissociation of CHBr(2)Cl at 248 nm by using cavity ring-down absorption spectroscopy. The quantum yield for the Br(2) elimination reaction is determined to be 0.05+/-0.03. The nascent vibrational population ratio of Br(2)(v=1)Br(2)(v=0) is obtained to be 0.5+/-0.2. A supersonic beam of CHBr(2)Cl is similarly photofragmented and the resulting Br atoms are monitored with a velocity map ion-imaging detection, yielding spatial anisotropy parameters of 1.5 and 1.1 with photolyzing wavelengths of 234 and 267 nm, respectively. The results justify that the excited state promoted by 248 nm should have an A(") symmetry. Nevertheless, when CHBr(2)Cl is prepared in a supersonic molecular beam under a cold temperature, photofragmentation gives no Br(2) detectable in a time-of-flight mass spectrometer. A plausible pathway via internal conversion is proposed with the aid of ab initio potential energy calculations. Temperature dependence measurements lend support to the proposed pathway. The production rates of Br(2) between CHBr(2)Cl and CH(2)Br(2) are also compared to examine the chlorine-substituted effect.     

Dispersed fluorescence spectroscopy of the GeCl2 A-X transition

The laser-induced fluorescence excitation spectrum of the GeCl(2) A-X transition at ultraviolet wavelengths (300-320 nm) was recorded in a direct current discharge supersonic free jet expansion. The excitation spectrum contains several sharp peaks and a congested diffuse structure. Dispersed fluorescence spectra following the excitation of these GeCl(2) ultraviolet bands were successfully acquired for the first time. The analysis of the dispersed fluorescence spectra reveals the detailed vibrational structure of the X (1)A(1) state. We have assigned the vibrational structures corresponding to different isotopomers (Ge(35)Cl(2), Ge(35)Cl(37)Cl, and Ge(37)Cl(2)). The vibrational fundamental frequencies were determined: 409 cm(-1) (symmetric stretch), 159 cm(-1) (bend), and 352 cm(-1) (antisymmetric stretch) for the X (1)A(1) state of GeCl(2). Vibrational parameters of the ground electronic state including vibrational frequencies, anharmonicity, and bend-stretch coupling constant were determined. Our dispersed fluorescence spectra also clarify the vibrational assignments of the hot bands and provide more experimental data for unraveling the nature of the congested diffuse structure at shorter wavelengths in the excitation spectrum.