The electronic spectrum of the C2P free radical and a Renner–Teller analysis of the Δ2 and X̃Π2 electronic states

Abstract

Subsequent to our spectroscopic detection of the C(2)X(X=P,As) free radicals [F. X. Sunahori et al., J. Am. Chem. Soc. 129, 9600 (2007)], we have studied the electronic spectrum of the (2)Delta(i)-X (2)Pi(r) system of the jet-cooled C(2)P free radical in the 490-630 nm region. The high-resolution laser-induced fluorescence spectrum of the two spin components of the 0(0) (0) band of (12)C(2)P has been recorded, and the rotational and spin-orbit coupling constants have been determined for both electronic states. The Renner-Teller effect has been observed in both the (2)Pi and the (2)Delta states, and the vibrational structure has been assigned. For the ground state, all of the observed levels up to 3500 cm(-1) were fitted with a standard Renner-Teller model. The excited (2)Delta state vibrational levels were successfully fitted using literature energy level expressions derived from perturbation theory, yielding vibrational and Renner-Teller parameters for both (12)C(2)P and (13)C(2)P. The molecular structure of C(2)P in the ground and excited states has also been estimated and compared to ab initio calculations and the geometries of similar molecules.

Electronic spectroscopy of the jet-cooled arsenic dicarbide (C2As) free radical

“…The ab initio value for the Renner-Teller parameter ͑0.57͒ is 18% lower than experiment, very similar to the 19% error obtained in similar calculations on the CCP free radical. 5 Finally it is noteworthy that the ground state x 23 anharmonicity constants determined from the experimental data take positive values for both 12 C 2 As and 13 C 2 As and that similar results are found for both the C 2 P and C 2 N radicals. 5,25 In conclusion, it should be emphasized that much remains to be done to fully explore the spectroscopy of the arsenic dicarbide free radical.…”

“…5 Finally it is noteworthy that the ground state x 23 anharmonicity constants determined from the experimental data take positive values for both 12 C 2 As and 13 C 2 As and that similar results are found for both the C 2 P and C 2 N radicals. 5,25 In conclusion, it should be emphasized that much remains to be done to fully explore the spectroscopy of the arsenic dicarbide free radical. A better method of synthesizing C 2 As would be highly desirable, as the weakness of our LIF signals precluded a more thorough study, particularly of the excited state Renner-Teller effect.…”

“…These frequencies can be used to calculate the Renner-Teller parameter and the average bending frequency 2 , as described in more detail elsewhere. 5 We have also calculated the vibrational frequencies of the 13 C 2 As isotopomer for comparison with experiment. The results of the ground state DFT predictions are summarized in Table I.…”

“…We came to similar conclusions in our recent study of the LIF spectrum of the CCP free radical. 5 The C u C bond length is calculated to decrease by 0.066 Å on electronic excitation to the 2 ⌬ state, which gives a value of 1.228 Å, only 0.026 Å longer than the triple bond in acetylene. The substantial increase observed in the 1 ͑C u C stretch͒ frequency on going from the ground to the excited state ͑from 1704.8 to 1851.3 cm −1 ͒ provides confirmation of the increase in the bond order.…”

“…4 We recently published a detailed analysis of the 2 ⌬ i -X 2 ⌸ r electronic transition of C 2 P in which we reported a rotational analysis of the 0 0 0 band and Renner-Teller analyses of the vibrational energy levels in the combining states. 5 An estimate of the ground state molecular structure from a combination of ab initio and experimental data led to the conclusion that the radical is best represented as C v C v P·.…”