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We present ab initio multireference configuration interaction (MRCI) calculations for the potential energy surfaces of HCCl in its three low-lying electronic states ( and ), and for the spin–orbit coupling between the and states. The two singlet states become a degenerate 1 ? state in collinear geometries. The potential energy surfaces are interpolated from 6075 MRCI energy points. The final surfaces are slightly adjusted using a coordinate and energy scaling approach. The resulting T e value is 2122.0?cm -1 for and 12209.8?cm -1 for . Vibrational energy levels of DCCl and HCCl are computed for the three states taking into account the Renner–Teller effect and the spin–orbit coupling. The calculated vibronic energy levels are in good agreement with the available experimental values. It is found that the spin–orbit effect is pronounced in the and states. [ABSTRACT FROM AUTHOR]

New spectra of methylene, CH[sub 2] , in the near infrared region of the singlet band system have been obtained. They were detected by laser transient absorption spectroscopy following excimer laser flash photolysis of ketene, CH[sub 2] CO, at 308 nm. The new data provide information on the nature and energies of rotational levels in three vibronic states that lie between approximately 11 500 and 13 000 cm[sup –1] above the zero point level of the lower, ã[sup 1] A[sub 1] , state. Taken together with previous measurements, a fairly complete picture of the vibronic energy levels of CH[sub 2] in this region can be built up. There is generally good agreement with the recent computational studies on the singlet states of CH[sub 2] , but some evidence for discrepancies for levels with K = 3 and higher near the minimum of the [sup 1] B[sub 1] potential surface. PACS No.: 33.20EaNous avons trouvé de nouveaux spectres du méthylène CH[sub 2] dans la région du proche infrarouge de la bande du singulet. Nous les avons observés par spectroscopie laser rapide suivant la photolyse du CH[sub 2] CO par impulsion d'un laser excimère à 308 nm. Ces nouvelles données nous renseignent sur la nature et l'énergie des niveaux rotationnels dans trois états vibroniques se trouvant approximativement entre 11 500 et 13 000 cm[sup –1] au dessus du point zéro de l'état ã[sup 1] A[sub 1] . Considérés avec des résultats déjà obtenus, ils nous fournissent une image assez complète des niveaux vibroniques du CH[sub 2] . L'accord avec les récentes études numériques sur les états singulets est très bon, mais des différences apparaissent pour les niveaux avec K = 3 près du minimum de la surface de potentiel [sup 1] B[sub 1] .[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Frequency comb-referenced measurements of sub-Doppler laser saturation dip absorption lines in the v 1 + v 3 band of acetylene near 1.5 μm are reported. These measurements include transitions involving higher rotational levels than previously frequency measured in this band. The accuracy of the measured frequencies is typically better than 10 kHz. Measurements of the observed sub-Doppler line widths as a function of pressure showed that the self-pressure-broadening coefficients are about 3.5 times larger than those derived from conventional pressure broadening of unsaturated Doppler-limited spectra. This is attributed to the contribution of velocity-changing collisions to the total dephasing rate in the low pressure sub-Doppler measurements. At higher pressures, when the homogeneous broadening becomes comparable to the typical Doppler shift per elastic collision, the velocity changing collisions cease to contribute significantly to the incremental pressure broadening. A time-dependent soft collision model is developed to illustrate the transition between low and high pressure regimes of sub-Doppler pressure-broadening. [ABSTRACT FROM AUTHOR]

The detection of 28 rotational lines in the bending fundamental band of DN+2 is reported. The spectra were obtained in a modulated discharge of D2 and N2 in a large hollow cathode which was cooled to liquid nitrogen temperature. Analysis leads to accurate values for the band origin and all of the major parameters describing the (0110) state of the ion. [ABSTRACT FROM AUTHOR]

The vibrational energy transfer in the azulene/CO2 system is studied. The vibrational excitation of CO2 and the relative populations of the CO2 ν2 and ν3 vibrational modes are studied experimentally by measuring the infrared emission intensities. (AIP) [ABSTRACT FROM AUTHOR]

Sub-Doppler, saturation dip, spectra of lines in the v1 + v3, v1 + 2v4, and v3 + 2v4 bands of 14NH3 have been measured by frequency comb-referenced diode laser absorption spectroscopy. The observed spectral line widths are dominated by transit time broadening and show resolved or partially-resolved hyperfine splittings that are primarily determined by the 14N quadrupole coupling. Modeling of the observed line shapes based on the known hyperfine level structure of the ground state of the molecule shows that, in nearly all cases, the excited state level has hyperfine splittings similar to the same rotational level in the ground state. The data provide accurate frequencies for the line positions and easily separate lines overlapped in Doppler-limited spectra. The observed hyperfine splittings can be used to make and confirm rotational assignments and ground state combination differences obtained from the measured frequencies are comparable in accuracy to those obtained from conventional microwave spectroscopy. Several of the measured transitions do not show the quadrupole hyperfine splittings expected based on their existing rotational assignments. Either the assignments are incorrect or the upper levels involved are perturbed in a way that affects the nuclear hyperfine structure. [ABSTRACT FROM AUTHOR]