C2H2 excited electronic state

CO is formed in three excited electronic states, namely, A X. (v < 6), e3 -(v <, 6), and d3A(t 9), with a maximum excitation energy corresponding to about 205 kcal/mole (8.89 eV) [175, 176]. Becker and Bayes substituted C302 for C2H2, and since the emission was unchanged and behaved identically as the flame conditions were altered, they proposed that the reaction... 

Data from the laser-induced fluorescence of C2 radicals obtained in the laboratory during 193 nm photolysis of C2H2 have been used to explain band profiles of C2 in the nucleus of comet Hyakutake, observed by the Hubble Space Telescope. In conjunction with ab initio computations, the data have led to the proposal that photolysis of C2H2, in the laboratory and in comets, proceeds by a sequential mechanism, first producing C2H and then C2. Two excited electronic states of C2H have been identified and 2 11) through which photodissociation in the second step occurs. Measurements of the kinetics and translational energy release in the near-UV photodissociation of the allyl radical have indicated that allene formation is the dominant H-loss reaction channel. ... 

Figure 2 Top photoelectron spectrum of ethylene. Bottom breakdown graph of ethylene determined by photoion-photoelectron coincidence measurements. Triangles and dots yields of C2H2" and C2H3 ions, respectively, obtained by collision experiments. The ground and excited electronic states of the C2H4 ion are denoted by X, A, B and C.

Figure 1. SEP spectrum of C2H2 at about 26,500 cm 1 of vibrational excitation in the ground electronic state. [Adapted from J. P. Pique, Y. Chen, R. W. Field and J. L. Kinsey, Phys. Rev. Lett. 58,475 (1987).] (a) Low-resolution ( 0.3 cm"1) spectrum (b) high-resolution ( 0.05 cm"1) spectrum Each feature in (a) is resolved into a series of lines. The overall envelope variation in intensity in (b) is the clump structure seen in (a).

EOM-CCSD gradients were implemented in 1994 by Stanton and Gauss. Recent applications to the Si surface of C2H2, the Si state of tetrazine, the excitation spetrum of C3H2, and a computation of force field for the first excited state of benzene" illustrate the power of gradient methods for electronically excited states. Table 12 compares calculated EOM-CCSD geometries, vibrational frequencies, and adiabatic excitation energies for the first excited state of a few diatomic molecules with available experimental data. 

The ground state C2H is a major primary product of the acetylene and lialoacetylene photolysis. Okabe (773) has observed the production of an electronically excited C2H that fluoresces in the region 4000 to above 5500 A m the vacuum ultraviolet photolysis of acetylene and bromoacetylene. The lifetime of this fluorescence is about 6 /rsec and the fluorescence is quenched icadily by C2H2, H2, N2, and Ar [Becker et al (81)]. On a theoretical basis, Sliih et al. (872a) speculate that the fluorescence arises from a transition X - X2I. 

Photochemistry. The Hg(3P,) sensitized photolysis ofC2H2 has produced benzene, hydrogen, and polymer [Shida et al. (872)]. Since the Hg(3Fi) state does not have sufficient energy required to dissociate the H—C2H bond, the products must be produced by reactions of an electronically excited C2H2. The photolysis of acetylene at 1849 A has produced hydrogen, ethylene, vinylacetylene, diacetylene, benzene, and solid polymers [Tsukada and Shida (979), Zelikoff and Aschenbrand (1082)]. 

HAAH molecules containing 10 valency electrons should be linear in their ground states. Those containing 12 electrons should be bent but planar cis- and /raMs-forms). Those containing 14 electrons should be bent and non-planar. The spectra of the isoelectronic molecules HCN and C2H2 are particularly discussed the first excited state of each should be non-linear. 

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