Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH
3
OH pumped by the
S-9P(31),18-10R(24),13-9R(26)
, and
13-9P(16)
CO
2
laser lines, plus an interesting speculation for the FIR line pumped by the
18-9P(12)
CO
2
line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm
^-1
from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three
¹⁶
O
¹²
C
¹⁸
O laser lines.