Laboratory detection of the 11←111 submillimeter wave transition of the H2D+ ion

Abstract

The 110←111 transition of H2D+ was detected in a dc discharge in Ar–H2–D2 mixtures with liquid nitrogen cooling and an applied axial magnetic field. The transition frequency was determined to be 372 421.380±0.100 MHz. This transition is expected to be the most favorable one for radioastronomical detection of this very crucial ion in the interstellar medium.

Accurate rest frequencies of submillimeter-wave lines of H2D+ and D2H+

“…The line center was measured by fitting observed line profiles to the Gaussian line profile, assuming that pressure broadening was negligible. The frequency for the H 2 D + line determined here was found to be close to the one measured by Warner et al [15], but the new measurement should be more accurate. The frequency for the 1 10 À 1 01 transition of D 2 H + turned out to be higher by 43 kHz than our own previous value.…”

“…Vastel et al [17] derived the v LSR for H 2 D + and D 2 H + to be 3.55 ± 0.02 and 3.76 ± 0.03 km/s, respectively, by using the laboratory frequencies [14,15,20]. They suggested that the difference of the v LSR for these two species might have been caused by possible systematic deviations, albeit small, of the laboratory measurements.…”

“…In the previous laboratory measurements of H 2 D + by two groups [14,15], they estimated the uncertainties for their line positions by taking into account possible systematic Doppler shifts caused by ion drift in the extended-negative glow discharges. We decided to measure the transition frequencies for both H 2 D + (J = 1 10 À 1 11 ) and D 2 H + (J = 1 10 À 1 01 ) species by reversing discharge polarity.…”

“…One of the relatively easily accessible millimeter-and submillimeter-wave transitions, the J = 1 10 À 1 11 around 372 GHz, was observed by two groups at almost the same time independently [14,15], and the transition frequency was determined to be 372421.34 (20) MHz by Bogey et al [14], and 372421.380(100) MHz by Warner et al [15]. Both laboratory experiments [14,15] were carried out with similar millimeter-wave spectrometer systems combined with extended-negative glow discharge setups [27]. Bogey et al estimated the uncertainty of the transition frequencies to be 200 kHz and the Wisconsin measurement gave the uncertainty of 100 kHz, taking the possible drift velocity of the ions due to the discharge electric field into account.…”

“…While, even at the very early stage of the development of astrochemistry, H 2 D + was recognized as an important species in the deuterium fractionation [12], the interstellar identification had not been made until 1999. The first astronomical identification of H 2 D + was brought about by Stark et al [13] by observing a submillimeter-wave line at 372.4 GHz toward a young stellar object NGC 1333 IRAS 4A, after more than a quarter of a century from the first laboratory measurements of this J = 1 10 À 1 11 transition [14,15]. Subsequently, Caselli et al [16] detected the H 2 D + line in a pre-stellar core L1544, followed by a detection toward another pre-stellar core 16293E [17].…”