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We present in this paper the results of high spectral resolution ($R$=88,100)spectroscopy at 4.7 $\mu$m with iSHELL/IRTF of hot molecular gas close to themassive binary protostar W3 IRS5. The binary was spatially resolved and thespectra of the two sources (MIR1 and MIR2) were obtained simultaneously for thefirst time. Hundreds of $^{12}$CO $\nu$=0-1, $\nu$=1-2 lines, and $\nu$=0-1transitions of the isotopes of $^{12}$CO were detected in absorption, and areblue-shifted compared to the cloud velocity $v_{LSR}=-$38 km/s. We decomposeand identify kinematic components from the velocity profiles, and applyrotation diagram and curve of growth analyses to determine their physicalproperties. Temperatures and column densities of the identified componentsrange from 30$-$700 K and 10$^{21}-$10$^{22}$ cm$^{-2}$, respectively. Ourcurve of growth analyses consider two scenarios. One assumes a foreground slabwith a partial covering factor, which well reproduces the absorption of most ofthe components. The other assumes a circumstellar disk with an outwarddecreasing temperature in the vertical direction, and reproduces the absorptionof all the hot components. We attribute the physical origins of the identifiedcomponents to the foreground envelope ($<$100 K), post-J-shock regions(200$-$300 K), and clumpy structures on the circumstellar disks ($\sim$600 K).We propose that the components with a J-shock origin are akin to water maserspots in the same region, and are complementing the physical information ofwater masers along the direction of their movements.

High-Resolution M-band Spectroscopy of CO towards the Massive Young Stellar Binary W3 IRS5