Table 1.

The CCSD(T)-F12/aug-cc-pVTZ Zero-Point ($R_{\alpha }$) Geometries, Vibrational Frequencies (Intensities ${}^a$ in Parentheses), and Spectroscopic Constants for ${}^3{B}_1$ He${}_2$H${}^{+}$, ${}^2{\mathsf{\Sigma }}_u$ He${}_2$${}^{+}$, and ${}^1{\mathsf{\Sigma }}_g^{+}$ HeHHe${}^{+}$.

		${}^2{\mathbf{\Sigma }}_{\mathit{u}}$He${}_2$${}^{+}$
	${}^3{\mathit{B}}_1$He${}_2$H${}^{+}$	This Work	Exp. ${}^{\mathit{b}}$	${}^1{\mathbf{\Sigma }}_{\mathit{g}}^{+}$HeHHe${}^{+}$
r${}_0$(He−He) Å	1.073 750	1.076 016	1.080	1.892 704
r${}_0$(H−X ${}^c$) Å	2.615 334			0.946 352
$A_0$ GHz	227.185
$B_0$ GHz	86.893	226.228	216.2	70.837
$C_0$ GHz	60.225
$\mu$ D	0.83
${\omega }_1$ cm${}^{-1}$	1706.4 (1)	1698.8	1698.5	1554.7 (2661)
${\omega }_2$ cm${}^{-1}$	324.1 (22)			955.1 (294)
${\omega }_3$ cm${}^{-1}$	186.4 (2)			1139.5
Zero-Point cm${}^{-1}$	1074.8	831.7		2261.4
${\nu }_1$ cm${}^{-1}$	1632.6	1625.0		1350.6
${\nu }_2$ cm${}^{-1}$	269.2			889.8
${\nu }_3$ cm${}^{-1}$	115.5			896.0
$2{\nu }_3$ cm${}^{-1}$	136.1

${}^a$ The double-harmonic intensities (in km/mol) and dipole moments are from MP2/aug-cc-pVDZ. The intensities for ${}^1{\mathsf{\Sigma }}_g^{+}$ HeHHe${}^{+}$ are from previous computations [15]; ${}^b$ Experimental results from extrapolations of ${}^3{\mathsf{\Pi }}_g$ He${}_2$ [44]; ${}^c$ X is the center of mass between the two helium atoms in ${}^3{B}_1$ He${}_2$H${}^{+}$, and X is He in ${}^1{\mathsf{\Sigma }}_g^{+}$ HeHHe${}^{+}$.