Molecular Hydrogen Absorption in the [CLC][ITAL]z[/ITAL][/CLC] = 1.97 Damped L[CLC]y[/CLC]α Absorption System toward Quasi-Stellar Object Q0013−004

We present a new ultraviolet spectrum of the quasi-stellar object Q0013-004 with 0.9 Å resolution obtained with the Multiple Mirror Telescope Blue Spectrograph. The υ = 0-0, 1-0, 2-0, and 3-0 Lyman bands of H 2 associated with the z = 1.9731 damped Lyα absorption-line system have been detected. The H 2 column density is N (H 2 ) = 6.9(±1.6) × 10 19 cm -2 , and the Doppler parameter b = 15 ± 2 km s -1 . The populations of different rotational levels are measured and used to derive the excitation temperatures. The estimated kinetic temperature T K ~ 70 K, and the total particle number density n ( H ) ~ 300 cm -3 . The UV photoabsorption rate β 0 ~ 6.7 × 10 -9 s -1 , about a factor of a few times greater than that in a typical diffuse Milky Way interstellar cloud. The total hydrogen column density is N (H) = 6.4(±0.5) × 10 20 cm -2 . The fractional H 2 abundance f = 2 N( H 2 )/[2 N (H 2 ) + N (H I)] ~ 0.22 ± 0.05 is the highest among all observed damped Lyα absorbers. The high fractional H 2 abundance is consistent with the inferred presence of dust and strong C I absorption in this absorber.