This is the second paper in a series aiming at searching for infrared pumping lines for galactic 1612 MHz OH masers .
Our paper I is devoted to the 34.6 \mu m absorption lines in ISO SWS spectra towards a large sample of galactic OH/IR sources .
This paper analyzes the 53.3 \mu m line in the ISO LWS spectra towards a similar sample of OH/IR sources .
A search with position radius of 1 arcmin in ISO Data Archive ( IDA ) results in 137 LWS spectra covering 53.3 \mu m associated with 47 galactic OH/IR sources and 4 ones associated with megamasers Arp 220 and NGC 253 .
( These two magamasers are included for comparison purpose only . )
Ten of these galactic OH/IR sources are found to show and another 5 ones tentatively show the 53.3 \mu m absorption while another 7 sources ( our group U1 and U2 sources ) highly probably do not show this line .
The source class is found to be correlated with the type of spectral profile : red supergiants ( RSGs ) and AGB stars tend to show strong blue-shifted filling emission in their 53.3 \mu m absorption line profiles while H II regions tend to show a weak red-shifted filling emission in the line profile .
GC sources and megamasers mainly show symmetrical profile in the line core while megamasers tend to show an additional absorption tail on the blue side of the line profile .
It is argued that the filling emission might be the manifestation of an unresolved half emission half absorption profile of the 53.3 \mu m doublet which might be produced by the transitions among the two levels : ^ { 2 } \Pi _ { 1 / 2 } ( J = 3 / 2 ) and ^ { 2 } \Pi _ { 1 / 2 } ( J = 5 / 2 ) and their closely related levels .
The 53.3 to 34.6 \mu m equivalent width ( EW ) ratio is close to unity for RSGs but much larger than unity for GC sources and megamasers while H II regions only show the 53.3 \mu m line .
The pump rate defined as maser to IR photon flux ratio is approximately 5 \% for RSGs .
The pump rates of GC sources are three order of magnitude smaller .
Both the large 53.3 to 34.6 \mu m EW ratio and the small pump rate of the GC OH masers reflect that the two detected ‘ pumping lines ’ in these sources are actually of interstellar origin .
The pump rate of Arp 220 is 32 \% —much larger than that of RSGs , which indicates that the contribution of other pumping mechanisms to this megamaser is important .
A handful of non–detections of the 34.6 or 53.3 \mu m line or both can be explained partly by the genuinely weakness of the OH masers and partly by some other mechanisms weakening the IR pumping lines , such as clumpy OH shell or limb filling emission .