Patrick Dupré

Study of singlet—triplet coupling in glyoxal by level anticrossing spectroscopy. V. Nature of singlet—triplet interaction

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Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. VI. Vibrational density and statistics of matrix elements versus energy

P. Dupre, R. Jost, M. Lombardi, P. G. Green, E. Abramson and R. W. Field, in preparation.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. IV. Theory of anticrossing position. Application to the measurement of triplet quantum numbers and rotational constants

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Continuous-wave cavity ringdown spectroscopy of the 8ν polyad of water in the 25195−25340cm−1 range

P.P. G. Green, PhD Thesis, MIT (1989). CAMBRIDGE MA (U.S.A.).

Quantum beat spectroscopic studies of Zeeman anticrossings in the Ã1Au state of the acetylene molecule (C2H2)

Abstract We observe in glyoxal cooled in a supersonic free jet the fluorescence of individual rotational levels of the S 1 state excited by a cw laser. We use the technique of singlet—triplet magnetic resonance near an anticrossing to measure matrix elements V 31 as a function of rotational quantum numbers N s , N t , K s , K t . The experimental results are compared with theoretical models of singlet—triplet couplings and we show that the spin-vibronic interaction is the dominant singlet—triplet interaction in glyoxal.

Rovibronic interactions in NO2 around 17 700 cm−1 observed by Zeeman effect and anticrossing experiments

Abstract By laser excitation of the rotationless level ( J = 0) of ten vibrational levels of the S 1 (A u ) state (0 0 , 7 2 , 5 1 , 8 1 , 6 1 7 1 , 4 1 , 8 1 7 2 , 2 1 , 8 1 4 1 and 2 1 7 2 ) of supersonic jet cooled glyoxal, we have obtained S 1 -T 1 anticrossing spectra using the homogeneous, high magnetic field (0–8 T) of a Bitter coil. As explained previously, V st is readily obtained from the width of an anticrossing. As triplet vibrational energy increases from 2776 (0 0 of S 1 ) to 4636 cm −1 (2 1 7 2 of S 1 ), the number of anticrossings increases from 38 (0 0 ) to 871 (2 1 7 2 ). The anticrossing density is related to the vibrational density of T 1 . The V st histrograms obtained for each vibrational level are very similar: p ( V st ) ∝ V −1−α st with 0.4 ⩽ α ⩽ 0.7. The more significant and surprising result is that V st > is independent of vibrational energy, even though the corresponding vibrational overlaps predicted a decrease in V st >, of at least two orders of magnitude between 0 0 and 2 1 7 2 . From V st statistics we determine ϱ V st > and ϱ V 2 st > which are the dominant factors for ISC (intersystem crossing). We predict that strong S-T mixing should occur above 6900 ± 500 cm −1 .

Quasiunimodal tunable pulsed dye laser at 440 nm: theoretical development for using a quad prism beam expander and one or two gratings in a pulsed dye laser oscillator cavity

Abstract We have performed anticrossing experiments in high magnetic fields on several rotational and vibrational singlet levels of glyoxal in a supersonic jet. We show that by analysis of these experiments, we can determine rotational quantum numbers, vibrational symmetry and rotational constants of the triplet level most efficiently coupled to the singlet laser-excited ones.

Study of Zeeman anticrossing spectra of the Ã1Au state of the acetylene molecule (C2H2) by Fourier transform: product ϱvibV〉 and isomerization barrier

State-of-the-art experiments and calculations are used to record and assign the data obtained in the weakly absorbing blue energy region of the H2O spectrum. Continuous-wave cavity ringdown absorption spectroscopy with Doppler resolution is used to probe the range from 25,195 to 25,470 cm(-1) with an absorption sensitivity of approximately 1 parts per 10(9) (ppb)/cm. 62 lines of the polyad nu(OH)=8 are reported, of which 43 are assigned using variational nuclear calculations. The study includes absorption line intensities (in the range of 10(-28)-10(-26) cmmolecule) for all lines and self-broadening pressure coefficient for a few lines. The newly obtained energy levels are also reported.

Characterization of a large single-triplet coupling in the à state of the acetylene molecule

Abstract We present results obtained by quantum beat spectroscopy of the gaseous acetylene molecule (HCCH). Spectra are presented for the rotationless levels ( J = K = N = I =0) of the A 1 A u ν 3 =0–2 states ( ν 3 is the trans-bending normal mode of the trans-bent excited state) and for the ( J = K = N =1, I =0 level of the ν 3 =0 level with the goal of obtaining information about singlet ∼ triplet interactions. The energy range thus sampled was from 42200 to 44300 cm −1 above the rotationless zero-point level of the X 1 Σ g + state and the magnetic field range was from 0 to 8 T. The centers of anticrossings, the coupling matrix elements, the Lande g factors, and the triplet lifetimes were mainly derived by fitting the measurements to a two-level model. Additional parameters were also introduced to take into account more complex interactions (up to a four-level model). The crucial discussion concerns the g l factors (local Lande factors) obtained, which were rarely equal to 2.0023, the value for a free electron, and the evolution of these g l factors as a function of the excitation energy. We interpret the observed behavior as due to strong electronic inter-triplet couplings (assumed here to be T 1 ∼ T 2 ) and weaker singlet ∼ triplet couplings (mainly S 1 ∼ T and secondarily S 0 ∼ T). We relate the present observations to previous observations obtained from Zeeman anticrossing spectra, which showed an unusually rapid increase of both the coupling matrix elements and the density of coupled levels as a function of the excitation energy [P. Dupre et al., Chem. Phys. 152 (1991) 293]. From our observations and in relation to the cis-linear-transisomerization barrier on a triplet surface, as we previously proposed, we suggest that the interactions between acetylene electronic states may be ordered according to their strengths: (S 0 ∼S 1 ⪡S 0 ∼T⪡S 1 ∼T⪡T 1 ∼T 2 ).