ancy is as follows. The previous set of D 1 S / u state constants Spectroscopic measurements of diatomic carbon, C 2 , are were determined by the direct fit of the upper and lower used to study comets (1-5), flames (6-8), the interstellar states in a nonleast squares iterative manner. In this paper, medium (9-12), and reaction dynamics (2,(13)(14)(15). These care was taken to ensure the statistical validity of the exmeasurements include absorption (10-12), emission (16tracted constants. A least squares algorithm was used to 18), LIF (1-2, 13-15), , and/or IR (22directly fit both the upper and lower states, and convergence 24) studies of the d 3 P g -a 3 P u (Swan), A 1 P u -X 1 S / g (Philwas observed with a more stringent tolerance. Precise moleclips), C 1 P g -A 1 P u (Deslandres-D'Azambuja), e 3 P g -a 3 P u ular constants for the X (23) and B (24) states were recently (Fox-Herzberg), D 1 S / u -X 1 S / g (Mulliken), E 1 S / g -A 1 P u determined by Bernath and co-workers. Their measurements (Freymark), b 3 S 0 g -a 3 P u (Ballik-Ramsay), and/or D 1 S / uwere the first experimental observations of the B state. Con-B 1 S / g , as well as several other electronic system(s). In all stants for the E and C states of C 2 are compiled in Ref. 32. of these studies, Franck-Condon factors (FCFs) are im-In this paper, we present the measured line positions and portant for the determination of band intensities and populaspectral analysis for the Mulliken and Freymark systems. tions. Literature reports of FCFs exist for all of these systems Molecular constants for the D and E states are also reported. with the exception of D-B. Ortenberg reported FCFs for The constants for the D state will be used to calculate FCFs the Swan and the Phillips systems (25). In a later study, for the Mulliken, D-B, D-C, and E-D electronic systems Halmann and Laulicht reported FCFs for the Swan, Phillips, of C 2 . All of these systems have in common the D 1 S / u state Fox-Herzberg, Deslandres-D'Azambuja, Mulliken, and are optically allowed transitions. To our knowledge, no Freymark, and Ballik-Ramsay systems of 12 C 2 and 13 C 2 literature report exists for the FCFs of the D-B and D-C (26). The FCFs reported by Halmann et al. and Ortenberg systems. Further, E-D and D-C transitions have not been were calculated by using Morse potential energy functions observed experimentally, and knowledge of FCFs for these in a formalism developed by Fraser and Jarmain (27). This systems will undoubtedly aid spectroscopists in the search method approximates the wavefunctions for the states infor and assignment of these bands. volved, hence, the FCFs are also approximate. Cooper and Nicholls (28-29) have used the more accurate Rydberg-
II. EXPERIMENTAL
Klein-Reese (RKR) method in their calculations of FCFs for all of the systems mentioned above, however, excluding Acetylene was used as the precursor of C 2 in the experithe D-B system due to the lack of experimental data. In a ments reported here and was passed through a dry ice/acemore recent study, FCFs for the Mulliken, Freymark, and tone trap to remove the small fraction of acetone present in the E-D systems of C 2 have been calculated using ab initio commercially available acetylene. The photochemistry of techniques (30).
C 2 H 2 has been extensively studied, and under two photon We recently reported revised molecular constants for the conditions at 193 nm, it is well known that C 2 is formed.
Only a brief description of the apparatus is given here D 1 S / u state determined from our high-resolution LIF measurements of the Mulliken system (31). The previously re-since it has been described in detail elsewhere (33)(34)(35).
The 130-liter stainless steel vacuum chamber from the previ-ported molecular constants are slightly different from the 200