Knowledge Bank

Since Herzberg and Johns reported the first observation of the CH$2$ ~{b}$\leftarrow$~{a} singlet-singlet transition, there have been numerous experimental and theorectical investigations of this system. Although the spectrum of the CH$2$ ~{b}$\leftarrow$~{a} transition has now been studied from the ultraviolet to the near-infrared (NIR), the origin band has not previously been observed due to a poor Franck-Condon factor as well as the lack of a convenient high resolution light source at approximately 1.2 $\mu$m. Here we report the successful observation of the origin band of the CH$2$ ~{b}$\leftarrow$~{a} system using a NIR-NIR double resonance technique. Based upon our results, effective rotational constants for the ~{b} (0,0,0) level can be determined. The level positions also provide information that can be used to improve the potential energy surface for the ~{b} state. Singlet CH$2$ is one of very few polyatomic molecules for which continuous high resolution data exist for rovibronic levels from the zero-point level of the ~{a} state through to predissociation. Acknowledgments: This work at Brookhaven National Laboratory was carried out under Contract No.DE-AC02-98CH10886 with the U.S. Department of Energy, and BCC is supported by National Science Council, Taiwan.