Predissociation of the 4pπL1Π Rydberg state of carbon monoxide

Vacuum Ultraviolet Photodissociation Branching Ratios of 12C16O, 13C16O, and 12C18O from 100500 to 102320 cm-1

The C⁺ ion photofragment spectra and photodissociation branching ratios into the two energetically available channels, C(¹D) + O(³P) and C(³P) + O(³P), have been obtained for the three CO isotopologues, ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O, in the vacuum ultraviolet range 100500-102320 cm^-1. The two vibronic states of ¹Σ⁺ symmetry, F(3dσ) ¹Σ⁺(υ' = 1) and J(4sσ) ¹Σ⁺(υ' = 0), predominantly dissociate into the lowest channel C(³P) + O(³P) through interactions with the repulsive D'¹Σ⁺ state. All three vibronic states of ¹Π symmetry, E'¹Π(υ' = 1, 2) and G(3dπ) ¹Π(υ' = 0), dissociate into both of the channels above. The photodissociation branching ratios into the channel C(¹D) + O(³P) for E'¹Π(υ' = 1, 2) are found to be independent of both the rotational quantum number and e/f parity, while those for G(3dπ) ¹Π(υ' = 0) strongly depend on the rotational quantum number, indicating very different predissociation pathways between the valence states E'¹Π(υ' = 1, 2) and the Rydberg state G(3dπ) ¹Π(υ' = 0). The potential energy curves of CO in the aforementioned energy range and below have recently been well constructed due to a series of interplays between high-resolution spectroscopic studies and theoretical calculations; the photodissociation branching ratios measured in this study can provide further benchmarks for future theoretical investigations which aim to understand the detailed predissociation dynamics of CO.

Reinvestigation of the Rydberg W1Π(ν = 1) level of 12C16O, 13C16O, and 12C18O through rotationally dependent photodissociation branching ratio measurements

A recent high resolution photoabsorption study revealed that the Rydberg W¹Π(ν = 1) level of carbon monoxide (CO) is perturbed by the valence E″¹Π(ν = 0) level, and the predissociation linewidth shows drastic variation at the crossing point due to the interference effect [Heays et al., J. Chem. Phys. 141(14), 144311 (2014)]. Here, we reinvestigate the Rydberg W¹Π(ν = 1) level for the three CO isotopologues, ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O, by measuring the rotationally dependent photodissociation branching ratios. The C⁺ ion photofragment spectra obtained here reproduce the recent high resolution photoabsorption spectra very well, including the presence of the valence E″¹Π(ν = 0) level. The photodissociation branching ratios into the spin-forbidden channel C(¹D) + O(³P) show sudden increases at the crossing point between the W¹Π(ν = 1) and E″¹Π(ν = 0) levels, which is in perfect accordance with the drastic variation of the linewidth observed in the recent spectroscopic study. Further analysis reveals that the partial predissociation rate into the lowest channel C(³P) + O(³P) shows a much more prominent decrease at the crossing point, which is caused by the interference effect between the W¹Π(ν = 1) and E″¹Π(ν = 0) levels, than that into the spin-forbidden channel C(¹D) + O(³P), and this is the reason of the sudden increase as observed in the photodissociation branching ratio measurements. We hope that the current experimental investigation will stimulate further theoretical studies, which could thoroughly address all the experimental observations in a quantitative way.

Strong and selective isotope effect in the vacuum ultraviolet photodissociation branching ratios of carbon monoxide

Rare isotope (¹³C, ¹⁷O and ¹⁸O) substitutions can substantially change absorption line positions, oscillator strengths and photodissociation rates of carbon monoxide (CO) in the vacuum ultraviolet (VUV) region, which has been well accounted for in recent photochemical models for understanding the large isotopic fractionation effects that are apparent in carbon and oxygen in the solar system and molecular clouds. Here, we demonstrate a strong isotope effect associated with the VUV photodissociation of CO by measuring the branching ratios of ¹²C¹⁶O and ¹³C¹⁶O in the Rydberg 4p(2), 5p(0) and 5s(0) complex region. The measurements show that the quantum yields of electronically excited C atoms in the photodissociation of ¹³C¹⁶O are dramatically different from those of ¹²C¹⁶O, revealing strong isotope effect. This isotope effect strongly depends on specific quantum states of CO being excited, which implies that such effect must be considered in the photochemical models on a state by state basis.

Branching Ratio Measurements of the Predissociation of 12C16O by Time-Slice Velocity-Map Ion Imaging in the Energy Region from 106 250 to 107 800 cm-1

Photodissociation of CO is a fundamental chemical mechanism for mass-independent oxygen isotope fractionation in the early Solar System. Branching ratios of photodissociation channels for individual bands quantitatively yield the trapping efficiencies of atomic oxygen resulting into oxides. We measured the branching ratios for the spin-forbidden and spin-allowed photodissociation channels of ¹²C¹⁶O in the vacuum ultraviolet (VUV) photon energy region from 106 250 to 107 800 cm^-1 using the VUV laser time-slice velocity-map imaging photoion technique. The excitations to four ¹Π bands and three ¹Σ⁺ bands of ¹²C¹⁶O were identified and investigated. The branching ratios for the product channels C(³P) + O(³P), C(¹D) + O(³P), and C(³P) + O(¹D) of these predissociative states strongly depend on the electronic and vibrational states of CO being excited. By plotting the branching ratio of the spin-forbidden dissociation channels versus the excitation energy from 102 500 to 110 500 cm^-1 that has been measured so far, the global pattern of the ¹Π-³Π interaction that plays a key role in the predissociation of CO is revealed and discussed.

Highly efficient solid-state distributed feedback dye laser based on polymer-filled nanoporous glass composite excited by a diode-pumped solid-state Nd:LSB microlaser

Realization of a compact, robust, highly stable, and efficient solid-state distributed feedback (DFB) dye laser based on pyrromethene 580-doped modified poly-(methyl methacrylate) embedded into nanoporous glass host is reported. A diode-pumped solid-state STA01SH-500 Nd:LSB microlaser (λ=532  nm; τ_0.5∼0.5  ns; E_P≤80  μJ; f≤500  Hz) is used as a pump source. When pumped well above threshold, a DFB laser emits a train of ultrashort pulses (τ≤1  ns; τ_0.5<0.5  ns; Δλ_0.5≤0.01  nm), while at excitation intensities not far from threshold, single transform-limited picosecond pulses (τ_0.5≤40  ps; τ_0.5Δν_0.5∼0.3), tunable from 541 to 598 nm, are generated. The DFB lasing efficiency reaches ∼60% upon an energy stability of ∼1.4% and an overall service life of the active element of ∼9×10⁷ laser shots. More than an order of magnitude increase in the temperature stability of a lasing wavelength as compared with ethanol solutions of laser dyes is practically demonstrated.

Isotopic dependence of the predissociations of the E(1)Π state of CO

The predissociations of the E(1)Π state of CO are again studied. They include both the background predissociation attributed to the continuum of the A(1)Π state and the accidental predissociation due to the k(3)Π state. They are calculated using a coupled equations method. The three components of the k state are introduced. These predissociations are studied for different isotopologues and are shown to decrease with increasing reduced mass, in agreement with the experimental results of Ubachs et al. [J. Chem. Phys. 113, 547 (2000)].

First analysis of the Herzberg (C1Σ+→ A1Π) band system in the less-abundant13C17O isotopologue

This work presents high-resolution emission spectra measurements of the Herzberg band system, which has not been observed and analysed in the¹³C¹⁷O isotopologue so far.

Branching ratio measurements for vacuum ultraviolet photodissociation of 12C16O

The branching ratios for the spin-forbidden photodissociation channels of (12)C(16)O in the vacuum ultraviolet (VUV) photon energy region from 102,500 (12.709 eV) to 106,300 cm(-1) (13.180 eV) have been investigated using the VUV laser time-slice velocity-map imaging photoion technique. The excitations to three (1)Σ(+) and six (1)Π Rydberg-type states, including the progression of W(3sσ) (1)Π(v' = 0, 1, and 2) vibrational levels of CO, have been identified and investigated. The branching ratios for the product channels C((3)P) + O((3)P), C((1)D) + O((3)P), and C((3)P) + O((1)D) of these predissociative states are found to depend on the electronic, vibrational, and rotational states of CO being excited. Rotation and e/f-symmetry dependences of the branching ratios into the spin-forbidden channels have been confirmed for several of the (1)Π states, which can be explained using the heterogeneous interaction with the repulsive D'(1)Σ(+) state. The percentage of the photodissociation into the spin-forbidden channels is found to increase with increasing the rotational quantum number for the K(4pσ) (1)Σ(+) (v' = 0) state. This has been rationalized using a (1)Σ(+) to (1)Π to (3)Π coupling scheme, where the final (3)Π state is a repulsive valence state correlating to the spin-forbidden channel.

Oxygen isotope fractionation in the vacuum ultraviolet photodissociation of carbon monoxide: wavelength, pressure, and temperature dependency

Several absorption bands exist in the vacuum ultraviolet (VUV) region of carbon monoxide (CO). Emission spectra indicate that these bands are all predissociative. Experimental results of CO photodissociation by vacuum ultraviolet photons (90 to 108 nm; ∼13 to 11 eV) from the Advanced Light Source synchrotron by measurement of the oxygen isotopic composition of the products are presented here. A large (few hundred per mil) range of oxygen isotopic compositions are observed in the CO photodissociation product and are wavelength dependent. Slope values (δ('17)O/δ('18)O) ranging from 0.72 to 1.36 were observed in the oxygen three-isotope space (δ('18)O vs. δ('17)O), which anti-correlated with increasing synchrotron photon energy, and indicates a dependency on the upper electronic state specific dissociation dynamics (e.g., perturbation and coupling associated with a particular state). An unprecedented magnitude in isotope fractionation was observed for photodissociation at 105 and 107 nm and is found to be associated with accidental predissociation of the vibrational states (ν = 0 and 1) for the upper electronic state E(1)Π. A significant temperature dependency in oxygen isotopic fractionation was observed, indicating a rotational level dependency in the predissociation process.

Branching ratio measurements of the predissociation of 12C16O by time-slice velocity-map ion imaging in the energy region from 108,000 to 110,500 cm(-1)

Direct branching ratio measurements of the three lowest dissociation channels of (12)C(16)O that produce C((3)P) + O((3)P), C((1)D) + O((3)P), and C((3)P) + O((1)D) are reported in the vacuum ultraviolet region from 108,000 cm(-1) (92.59 nm) to 110,500 cm(-1) (90.50 nm) using the time-slice velocity-map ion imaging and nonlinear resonant four-wave mixing techniques. Rotationally, resolved carbon ion yield spectra for both (1)Σ(+) and (1)Π bands of CO in this region have been obtained. Our measurements using this technique show that the branching ratio in this energy region, especially the relative percentages of the two spin-forbidden channels, is strongly dependent on the particular electronic and vibrational energy levels of CO that are excited.

Rydberg-valence interactions of CO, and spectroscopic evidence characterizing the C' 1Sigma+ valence state

Rotationally cold absorption and two-photon ionization spectra of CO in the 90-100 nm region have been recorded at a resolution of 0.3-1.0 cm(-1). The analyses of up to four isotopomers seek to clarify the observations in regions where the Rydberg levels built on the ground state X (2)Sigma(+) of the ion interact with valence states of (1)Sigma(+) and (1)Pi symmetry. Previous observations of the 3ssigma, B (1)Sigma(+) Rydberg state, reviewed by Tchang-Brillet et al. [J. Chem. Phys. 96, 6735 (1992)], have been extended to energies above its avoided crossing with the repulsive part of the D(') (1)Sigma(+) valence state where resonances of varying intensities and widths have been attributed to the fully coupled 3ssigma or 4ssigma and D(') potentials, and where the B state approaches a second avoided crossing with the C(') (1)Sigma(+) valence state [Cooper and Kirby, J. Chem. Phys. 87, 424 (1987); 90, 4895 (1989); Chem. Phys. Lett. 152, 393 (1988)]. Fragments of a progression of weak and mostly diffuse bands, observed for all four isotopomers, have been assigned to the C(')<--X transition. The least-squares modeling of the 4p and 5p complexes reveals the 3ppi, E (1)Pi Rydberg state to be one of the perturbers, violating the Deltav=0 selection rule for Rydberg-Rydberg interactions on account of its rapid transition with increasing v from Rydberg to valence state. A second (1)Pi perturber, very loosely bound and clearly of valence type, contributes to the confusion in the published literature surrounding the 5p, v=0 complex.

Lifetime and predissociation yield of 14N2 b 1Πu(v=1)

The lifetime of the b 1Piu(v=1) state in 14N2 has been determined experimentally using a laser-based pump-probe scheme and an exceptionally long lifetime of 2.61 ns was found. Semiempirical close-coupling calculations of the radiative lifetime, which include Rydberg-valence interactions in the singlet manifold, are consistent with this large value, giving a value of 3.61 ns and suggesting a predissociation yield of approximately 28% for this level of the b state.