Spectroscopic Constants, Abundances, and Opacities of the TiH Molecule

Abstract

Using previous measurements and quantum chemical calculations to derive the molecular properties of the TiH molecule, we obtain new values for its ro-vibrational constants, thermochemical data, spectral line lists, line strengths, and absorption opacities. Furthermore, we calculate the abundance of TiH in M and L dwarf atmospheres and conclude that it is much higher than previously thought. We find that the TiH/TiO ratio increases strongly with decreasing metallicity, and at high temperatures can exceed unity. We suggest that, particularly for subdwarf L and M dwarfs, spectral features of TiH near $\sim$0.52 \mic, 0.94 \mic, and in the $H$ band may be more easily measureable than heretofore thought. The recent possible identification in the L subdwarf 2MASS J0532 of the 0.94 \mic feature of TiH is in keeping with this expectation. We speculate that looking for TiH in other dwarfs and subdwarfs will shed light on the distinctive titanium chemistry of the atmospheres of substellar-mass objects and the dimmest stars.Comment: 37 pages, including 4 figures and 13 tables, accepted to the Astrophysical Journa

Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres

“…A number of values of A v 0 v 00 for both electronic transitions are listed in Table 2 of Burrows et al (2005). Unlike TiO, where data on several isotopic versions are available, for TiH, only data on the main isotopic version 48 TiH are available, so the isotopic shifts for the forms containing 46 Ti, 47 Ti, 49 Ti, and 50 Ti, have to be calculated, using equation (7), and the methods briefly discussed in x 2.…”

“…Unlike TiO, where data on several isotopic versions are available, for TiH, only data on the main isotopic version 48 TiH are available, so the isotopic shifts for the forms containing 46 Ti, 47 Ti, 49 Ti, and 50 Ti, have to be calculated, using equation (7), and the methods briefly discussed in x 2. The quantum numbers of the levels involved are known, together with the vibrational and rotational constants from Burrows et al (2005) for the three electronic states, of which the pair X and A or X and B participate in a given transition. Although the shift of the lines of TiD is large, even when deuterium has not been destroyed by nuclear burning, at best, it has an abundance of about 5 orders of magnitude below normal hydrogen, so its isotopic shift, and equivalently, those of the other hydrides, is not required.…”

“…The partition function can be calculated from equation (3) using the spectroscopic data of the 15 electronic states listed in Tables 11 and 12 of Burrows et al (2005), including the X, A, and B states used to calculate the opacity. Since the energy levels of the four spin substates of the X electronic state are available, these can be treated as four separate states for calculating the partition function, so the sum can be performed over 18 states.…”

“…Both have very similar properties. This is followed by x 2.3, where we discuss the metal hydrides TiH ( Burrows et al 2005), CrH ( Burrows et al 2002), FeH (Dulick et al 2003), MgH (Skory et al 2003;Weck et al 2003a), and CaH (Leininger & Jeung 1995;Weck et al 2003b), which all have similar properties.…”

Detection of anhydrous hydrochloric acid, HCl, in IRC +10216 with the HerschelSPIRE and PACS spectrometers

“…The thermochemical data of the included molecules were taken from Chase (1998), with updates for various species being taken from the recent literature. In particular, the thermochemical data of TiH were updated according to Burrows et al (2005). The adopted parameters for IRC +10216 are presented in Agúndez & Cernicharo (2006).…”