  We present near-infrared spectroscopy of ten weak emission-line quasars
(WLQs) at redshifts of $z\sim2$, obtained with the Palomar 200-inch Hale
Telescope. WLQs are an exceptional population of type 1 quasars that exhibit
weak or no broad emission lines in the ultraviolet (e.g., the C IV $\lambda
1549$ line), and they display remarkable X-ray properties. We derive
H$\beta$-based single-epoch virial black-hole masses (median value $\rm 1.7
\times 10^{9} M_{\odot}$) and Eddington ratios (median value $0.5)$ for our
sources. We confirm the previous finding that WLQ H$\beta$ lines, as a major
low-ionization line, are not significantly weak compared to typical quasars.
The most prominent feature of the WLQ optical spectra is the universally
weak/absent [O III] $\lambda 5007$ emission. They also display stronger optical
Fe II emission than typical quasars. Our results favor the super-Eddington
accretion scenario for WLQs, where the weak lines are a result of a soft
ionizing continuum; the geometrically thick inner accretion disk and/or its
associated outflow is responsible for obscuring the nuclear high-energy
radiation and producing the soft ionizing continuum. We also report candidate
extreme [O III] outflows (blueshifts of $\approx 500$ and $\rm 4900 km s^{-1}$)
in one object.
