the mid-L dwarfs. The young L2 dwarf, G196-3B, exhibits narrow potassium lines without extensive pressure-broadened wings, indicative of a lower gravity atmosphere. Kelu-1AB, another L2, has exceptionally broad infrared lines, including FeH and H$_{2}$O features, confirming its status as a rapid rotator. In contrast to other late T objects, the peculiar T6 dwarf 2MASS 0937+29 displays a complete absence of potassium even at high resolution, which may be a metallicity effect or a result of a cooler, higher-gravity atmosphere.'
author:
- '[IAN S. MCLEAN, L. PRATO, MARK R. MCGOVERN, ADAM J. BURGASSER, J. DAVY KIRKPATRICK, EMILY L. RICE AND SUNGSOO S. KIM]{}'
title: 'THE NIRSPEC BROWN DWARF SPECTROSCOPIC SURVEY II: HIGH-RESOLUTION J-BAND SPECTRA OF M, L and T DWARFS[^1]'
---

Introduction
============

With effective temperatures $\la$ 2200 K, the cool atmospheres of L and T dwarfs generate complex spectra that are rich in molecular features, especially at near-infrared (NIR) wavelengths where ro-vibrational transitions of many molecules dominate. Fortunately, these cool, very low luminosity objects are also brightest in the NIR. Until recently, most infrared spectroscopic investigations of L and T dwarfs have concentrated on the identification of strong, broad spectral features, useful for the establishment of spectral classification, and have 