IBM Res. Rept. RW118, (1969). G. Breit, Rev. Mod. Phys. 5, 91 (1933); M. Z. Rose and R. L. Carovillano, Phys. Rev. 122, 1185 (1961);P. A. Franken, ibid. 121, 1508A. Franken, ibid. 121, (1961;H. H. Stroke, G. Fulop, S. Klepner, and O. Redi, Phys. Rev. Letters 21, 61 (1968). The diagonalization is performed within the manifold of the excited state only, since Zq. (1) is independent of the basis states ) m) so long as they span the space of the ground state. That is, [m) enters Eq. (1) only as g [ m) (m I which is invariant in a unitary transformation to another basis.
In methylene, the rotational levels of the ã 1A1 (0,0,0) and (0,1,0) vibronic states are so heavily perturbed by nearby rovibrational levels of the ground triplet state (X̃ 3B1) that standard rotation–vibration Hamiltonians do not provide a satisfactory fit or any indication as to which levels are strongly perturbed and which are less perturbed. Recent spectroscopic and theoretical work gives triplet state term values and the singlet–triplet energy difference with an accuracy of a few tens of wave numbers. Using these term values and ab initio spin-orbit matrix elements it is shown that all Ka=1, 3, and 4 levels of 1A1 (0,0,0) and all Ka=1 levels of 1A1 (0,1,0) are strongly perturbed by 3B1 (0,v2,0) levels with 2≤v2≤4. Individual levels in the other Ka stacks are also perturbed but most can be fit satisfactorily with a Watson Hamiltonian. The shifts between the observed term values and those calculated from the Watson Hamiltonian are reproduced in each Ka stack by a spin-orbit matrix element value only 5%–30% larger than the ab initio value. Over 60% of the measured term values show shifts greater than 0.2 cm−1. Shifts of the 322 and 000 levels can only be explained by interaction with levels in either (1,0,0) or (0,0,1) states; possible values for the vibrational frequencies of ν1 and ν3 of 3B1 are given. Molecular constants for 1A1 (0,0,0) and (0,1,0) are derived and quantitative estimates of spin-orbit mixing for individual levels of 1A1 (0,0,0) and (0,1,0) are given. From a chemical point of view singlet methylene is never in a pure spin state and always has some triplet character in its wave function. These data provide a basis for proper modeling of the kinetics of chemical reactions of ‘‘singlet’’ and ‘‘triplet’’ methylene species and their interconversion by ‘‘intersystem crossing.’’
Laser-induced fluorescence (LIF) has been used to measure rotational temperatures, T R , of the aniline molecule in axissymmetric and planar pulsed supersonic expansions of He, Ne, and Ar. The rotational contours of the 0-0 band of the ' B~ +-' A , transition of aniline were measured by LIF and were fitted by computer-simulated rotational contours, resulting in the determination of T R . For axis-symmetric jets expanded from a 0.06 cm nozzle at stagnation pressures p = 100-2300 Torr, we find 7 '~ to vary from 15 2 2 K to 2.2 + 0.2 K. The degree of rotational cooling increases in the order of He 5 Ne e Ar.The pressure dependence of T R on p is T R a p-077-0.0S for Ar (in the range p = 100-1000 Torr) and T n U 3 i 0 0 5 for He (in the range p = 300-2300 Torr), manifesting the implications of the velocity slip effect. Evidence for extensive formation of van der Waals complexes in the aniline-Ar system a t p 2 1000 Torr was inferred from the saturation of TR with increasing p in this range. In planar supersonic jets of Ar expanded from a 0.2 X 35 mrn nozzle slit at p = 5-200 Torr, the rotational temperature varied in the range TR = 90 + 10 K to 12 C 2 K, exhibiting thedependence TR x~-' .~~~~~~~~' .Additional diagnostic information on planar jets was obtained for the dependence of the rotational temperature on the distance from the nozzle slit.La fluorescence induite par laser a Cte utilisee pour mesurer les tempkratures rotationnelles, TR, de la molkcule d'aniline dans des expansions supersoniques pulskes, a symktrie axiale ou plane, de He, Ne at Ar. On a mesurC les contours rotationnels de la bande 0-0 dc la transition ' B z t ' A , de I'aniline. et ces mesures ont etk ajustees sur des contours rotationnels obtenus par simulation sur ordinateur, afin de dkterminer TR. Dans le cas de I'expansion de jets ? I symetrie axiale sortant d'un orifice de 0,06 crn a des pressions de stagnation p = 100-2300 Torr, nous trouvons que TR varie de 15 t 2 K a 2.2 t 0,2 K. Le degrC de refroidissement rotationnel croit dans I'ordre He 5 Ne e Ar. La variation de TR en fonction de la pression p est donnee par TR a p-".77.0.0s pour Ar (dans I'intervalle p = 100-1000 Tom), et par T R p~~" -8 3 1 -0~0 5 pour He (dans I'intervalle p = 300-2300 Torr), manifestant les implications de I'effet de glissement de vitesse. La saturation de TR avec I'accroissement de la pression au-dessous de 1000 Tom prouve qu'il y a, a des pressions de cet ordre, formation abondante de complexes de Van der Waals dans le systeme aniline-Ar. Dans le cas des jets supersoniques plans sortant d'une fente de 0,2 X 35 mm 5 5-200Tom, la tempkrature rotationnelle varie dans un intervalle allant de TR = 90 + 10 K a TR = 12 + 2 K, avec une dependance de la pression donnee par TR a 1 1 -~.~~~=~~. '~) . Comme information additionnelle pour le diagnostic des jets plans, on a determink I'effet de la distance 6 la fente sur la temperature rotationnelle.[Traduit par le journal]Can.
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