Deuterated methanol toward NGC 7538-IRS1

We investigate the deuteration of methanol towards the high-mass star-forming region NGC 7538-IRS1. We carried out a multi-transition study of CH3OH, (CH3OH)-C-13, and the deuterated flavors, CH2DOH and CH3OD, between 1.0 and 1.4 mm with the IRAM-30 m antenna. In total, 34 (CH3OH)-C-13, 13 CH2DOH lines and 20 CH3OD lines spanning a wide range of upper-state energies (E-up) were detected. From the detected transitions, we estimate that the measured D/H does not exceed 1%, with a measured CH2DOH/CH3OH and CH3OD/CH3OH of about (32 +/- 8) x 10(-4) and (10 +/- 4) x 10(-4), respectively. This finding is consistent with the hypothesis of a short-timescale formation during the pre-stellar phase. We find a relative abundance CH2DOH/CH3OD ratio of 3.2 +/- 1.5. This result is consistent with a statistical deuteration. We cannot exclude H/D exchanges between water and methanol if water deuteration is of the order 0.1%, as suggested by recent Herschel observations.