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The study stated that the b(super ~) (super 1) B(sub 1) - a(super ~)(super 1)A(sub 1) spectrum of methylene between 9317 and 9610 cm(super -1) were recorded using frequency-modulated diode laser absorption spectroscopy. A comparison of the results of the recent high-level quantum chemical calculations suggested that the further refinement of the potential energy surface of the b(super ~) state near its equilibrium would be done.

The origin of the cation ground electronic state was used to record the photoinduced Rydberg ionization spectrum of third excited electronic state of phenylacetylene cation. It was found that the vibrational structure of C state of phenylacetylene cation is well resolved, although the line widths are not quite as narrow as other substituted benzenes.

New spectra of methylene, CH2, in the near-infrared are obtained following 308 nm photolysis of ketene, CH2CO. Nascent photofragment Doppler spectra and thermalization kinetics vary systematically with the energy of the absorbing level, providing additional information to support or refute spectroscopic assignments made on the basis of the frequency measurements and combination differences.

The photodissociation experiments on CHBr3 at 248 nm were performed using VUV ionization photofragment translational spectroscopy. It is concluded that the most important photodissociation channel of CHBr3 in the UV region is C-Br bond breaking.

The kinetics and product distribution for the reaction of methyl radicals, CH3, with ground-state O(3P) oxygen atoms were studied. This reaction was investigated with an apparatus which combined a tubular flow reactor and a time-of-flight mass spectrometer, using a hollow-cathode lamp for photoionization. In addition to the dominant product, formaldehyde (CH2O), carbon monoxide was detected as a product with a yield of 0.17 +/- 0.11.

Excitationof phenylacetylene (PA) and benzonitrile to their lowestsinglet states in a molecular beam has previously been shown to immediately(only during the 8 ns laser pulse) result in long-lived species withlow ionization potentials (Hofstein, J.; Xu, H.; Sears, T.; Johnson,P.M. J. Phys. Chem. A2008,112,1195–1201). Using the fragmentation of ionsproduced by photoionization at various times after initial excitationas a diagnostic for molecular geometry evolution, the long-lived speciesin phenylacetylene is shown to be a PA state (most likely a triplet)rather than an isomer. Delayed fluorescence and a delayed photoelectronsignal indicative of S1are also seen, indicating a singlet–tripletmixing process that is not quite in the statistical-coupling limitand is parallel to the long-lived species channel. Electronic structurecalculations indicate that the lowest triplet state of phenylacetyleneis nonplanar with the ethynyl group bent in a trans-configurationout of the plane of the ring. The substituent π-electrons aresignificantly conjugated into the ring, resulting in a tendency towarda quinoidal structure, which may be related to the unusual excitedstate stability. These molecules constitute the first members of anew class of excited state behaviors. [ABSTRACT FROM AUTHOR]

New spectra of methylene, CH2, in the near-infrared have been obtained following 308 nm photolysis of ketene, CH2CO. Nascent photofragment Doppler spectra and thermalization kinetics vary systematically with the energy of the absorbing level, providing additional information to support or refute spectroscopic assignments made on the basis of the frequency measurements and combination differences. New assignments in the 10800 cm-1 region extend to higher rotational levels than before and provide new spectroscopic term values for some CH2 ãA1 state levels. The number and intensity distribution of unassigned lines in the spectrum is consistent with the expected transitions from vibrationally excited and high rotational levels of the ã1A1 state and transitions due to 13CH2 in natural abundance, and does not require a significant contribution from additional transitions arising from triplet-state perturbations. [ABSTRACT FROM AUTHOR]

The P(11) line of the ν1 + ν3 combination band of C2H2 was studied using an extended cavity diode laser locked to a frequency comb. Line shapes were measured for acetylene and nitrogen gas mixtures at a series of temperatures between 125 and 296 K and total pressures up to 1 atm. The data were fit to two speed-dependent line shape models and the results were compared. Line shape parameters were determined by simultaneously fitting data for all temperatures and pressures in a single multispectrum analysis. Earlier pure acetylene measurements [Cich et al. Appl. Phys. B 2012, 109, 373-38] were incorporated to account for self-perturbation. The resulting parameters reproduce the observed line shapes for the acetylene-nitrogen system over the range of temperatures and pressures studied with average root-mean-square observed-calculated errors of individual line measurement fits of approximately 0.01% of maximum transmission, close to the experimental signal-to-noise ratios. Errors in the pressure measurements constitute the major systematic errors in these measurements, and a statistical method is developed to quantify their effects on the line shape parameters for the present system.

Selected isolated rotational transitions in the 1-0 band of the red A(2)Π-X (2)Σ(+) system in CN have been recorded with transient frequency modulation spectroscopy as a function of argon pressure up to 0.2 atm at room temperature. Line shapes were fit using Fourier transforms of a parametrized time correlation function, including Doppler and velocity-dependent collisional broadening, and collisional shifts. Deviations from Voigt line shapes can be equally well fit by modeling the narrowing with a speed-dependent collision model or with a velocity-changing collisional narrowing model. Pressure broadening coefficients were observed with little rotational state dependence, in the range of 0.070-0.075 cm(-1) atm(-1). In contrast, stronger and qualitatively different rotational state dependences are observed for both pressure-dependent blue shift coefficients and the narrowing parameters. No asymmetry in the pressure broadened lines was observed.

The sensitivity of vibronic calculations to electronic structure methods and basis sets is explored and compared to accurate relative intensities of the vibrational bands of phenylacetylene in the S(1)(A(1)B(2)) ← S(0)(X(1)A(1)) transition. To provide a better measure of vibrational band intensities, the spectrum was recorded by cavity ringdown absorption spectroscopy up to energies of 2000 cm(-1) above the band origin in a slit jet sample. The sample rotational temperature was estimated to be about 30 K, but the vibrational temperature was higher, permitting the assignment of many vibrational hot bands. The vibronic structure of the electronic transition was simulated using a combination of time-dependent density functional theory (TD-DFT) electronic structure codes, Franck-Condon integral calculations, and a second-order vibronic model developed previously [Johnson, P. M.; Xu, H. F.; Sears, T. J. J. Chem. Phys. 2006, 125, 164331]. The density functional theory (DFT) functionals B3LYP, CAM-B3LYP, and LC-BLYP were explored. The long-range-corrected functionals, CAM-B3LYP and LC-BLYP, produced better values for the equilibrium geometry transition moment, but overemphasized the vibronic coupling for some normal modes, while B3LYP provided better-balanced vibronic coupling but a poor equilibrium transition moment. Enlarging the basis set made very little difference. The cavity ringdown measurements show that earlier intensities derived from resonance-enhanced multiphoton ionization (REMPI) spectra have relative intensity errors.

The origin band in the b̃(1)B(1)-ã(1)A(1) transition of CH(2) near 1.2 μm has been recorded at Doppler-limited resolution using diode laser transient absorption spectroscopy. The assignments of rotational transitions terminating in upper state levels with K(a) = 0 and 1, were confirmed by ground state combination differences and extensive optical-optical double resonance experiments. The assigned lines are embedded in a surprisingly dense spectral region, which includes a strong hot band, b̃(0,1,0) K(a) = 0 - ã(0,1,0) K(a) = 1 sub-band lines, with combination or overtone transitions in the ã(1)A(1) state likely responsible for the majority of unassigned transitions in this region. From measured line intensities and an estimate of the concentration of CH(2) in the sample, we find the transition moment square for the 0(00) ← 1(10) transition in the b̃(1)B(1)(0,0,0)(0)-ã(1)A(1)(0,0,0)(1) sub-band is 0.005(1) D(2). Prominent b̃(1)B(1)(0,1,0)(0)-ã(1)A(1)(0,1,0)(1) hot band lines were observed in the same spectral region. Comparison of the intensities of corresponding rotational transitions in the two bands suggests the hot band has an intrinsic strength approximately 28 times larger than the origin band. Perturbations of the excited state K(a) = 0 and 1 levels are observed and discussed. The new measurements will lead to improved future theoretical modeling and calculations of the Renner-Teller effect between the ã and b̃ states in CH(2)., (© 2011 American Chemical Society)

The vibrational structure of the S(1)-S(0) electronic band of phenylacetylene has been recorded by 1 + 1 resonance-enhanced multiphoton ionization, accompanied by slow electron velocity map imaging photoelectron spectroscopy at each resonant vibrational band. Assignments of the S(1) vibrations (up to 2000 cm(-1) above the band origin) are based upon the relative intensities of the vibronic bands calculated by complete second-order vibronic coupling, vibration-rotation (Coriolis and Birss) coupling calculations, and the vibrational structure of the S(1) resonant photoelectron spectra. Although this is an allowed electronic transition, the relative intensities of the a(1) bands are often largely determined by vibronic coupling rather than simple Franck-Condon factors, and second-order coupling is substantial. Nonsymmetric vibrations have intensities obtained through either vibronic or Coriolis coupling, and the calculations have been instrumental in discriminating between alternate possibilities in the assignments. Strong vibronic effects are expected to be present in the spectra of most monosubstituted benzenes, and the calculations presented here show that theoretical treatments based upon electronic structure calculations will generally be useful in the analysis of their spectra.

In an attempt to characterize the state interactions near the dissociation energy of singlet methylene, the near ultraviolet band system of singlet methylene has been studied using a laser optical-optical double resonance scheme. Spectra terminating in several, previously unobserved, higher bending levels of the c(1)A1 state have been detected. The highest energy band has simple rotational structure with lifetime broadened lines and is observed near 32300 cm(-1), which is 500 cm(-1) above the current best estimate for the singlet bond dissociation energy to CH((2)Pi) + H((2)S). Two lower energy bands exhibit a proliferation of rotationally-labeled double-resonance lines in the vicinity of the bright c(0,12,0) and c(0,13,0) bending levels, indicating that at least 7 and 9 strongly coupled vibronic states participate in each of these bands, respectively. The additional states may be associated with kinks in the adiabatic c state potential along the asymmetric stretching coordinate associated with interactions among c(1)A', a(1)A', and 3(1)A' states, as described by Ostojic (J. Mol. Spectrosc. 2002, 212, 130). There is no evidence for lifetime broadening below the singlet dissociation energy; hence we conclude that coupling of spectroscopically accessible singlet CH2 levels to the triplet manifold is very small.

The photoinduced Rydberg ionization spectrum of the third excited electronic state of phenylacetylene cation was recorded via the origin of the cation ground electronic state. The origin of this state is 17 834 cm(-1) above the ground state of the cation, and the spectrum shows well-resolved vibrational features to the energy of 2200 cm(-1) above this. An assignment of the vibrational structure was made by comparison to calculated frequencies and Franck-Condon factors. From the assignments, and electronic structure considerations, the electronic symmetry of the C state is established to be (2)B(1).