Observation of a strong vibrational population inversion by CO laser excitation of pure solid carbon monoxide

Under irradiation of a pure solid CO sample at low temperature by a CW CO laser beam,
¹³
C
¹⁶
O,
¹²
C
¹⁸
O and
¹³
C
¹⁸
O molecules are excited to high vibrational levels, up to
\upsilon = 23
, and a strong population inversion is observed. The
¹²
C
¹⁶
O molecules are pumped to the
\upsilon = 1
level by laser line absorption in the low frequency phonon sideband, and the vibrational energy is subsequently transferred to the other isotopes. Quantum yield, efficiency, and heat release are discussed to clarify the mechanism.