We show that ultrashort pulse strong field multiphoton ionization efficiently produces metastable highly charged molecules such as metastable diatomic trications ${\mathrm{I}}_2^{3+}$, ${\mathrm{Br}}_2^{3+}$, and ${\mathrm{Cl}}_2^{3+}$. The efficiency of stable trication production decreases rapidly with increasing pulse duration. Weak pre- or post-pulse irradiation also prevents efficient production or survival of trications. We propose strong-field femtosecond Raman spectroscopy to determine trication vibrational frequencies.

• Received 28 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.81.2217